How to tell if a number is mobile or VoIP

Ben Argeband, Founder & CEO of Heartbeat.ai — Decision-based; no telecom deep dive.

Who this is for

Recruiters who need to decide whether SMS is appropriate, avoid wasted dials, and keep outreach compliant. If you’re trying to get to a real conversation faster (without texting a shared office line), this is the routing playbook.

Quick Answer

Core Answer

Classify the line type, validate by behavior, then route: mobile can support SMS; VoIP/landline usually call/email first. Porting makes it probabilistic.

Key Insight

Line type changes expectations and reachability. Number porting blurs signals, so treat “mobile vs VoIP” as a routing input, not a guarantee.

Best For

Recruiters choosing whether SMS is appropriate and avoiding wasted dials.

Compliance & Safety

This method is for legitimate recruiting outreach only. Always respect candidate privacy, opt-out requests, and local data laws. Heartbeat does not provide medical advice or legal counsel.

• 60-second tells (practical)
  • Personal voicemail greeting with a name usually behaves like a personal line.
  • IVR menus (“press 1…”) usually behave like a business system (often VoIP).
  • Front desk/staff answers are a shared-line signal—don’t treat it like a personal mobile.
  • “Wrong person” responses mean reassigned/shared—suppress and refresh.
  • If detection says mobile but you consistently hit an IVR, suspect number porting or business routing.

• SMS red flags (pause texting)
  • Any IVR/operator greeting on the number.
  • Staff replies or a shared inbox tone (“Scheduling,” “Front Desk,” “Team”).
  • Wrong-party indicators or identity uncertainty.
  • Any opt-out request (suppress immediately).

Framework: The Line Type Routing Framework: Detect → Validate → Route → Refresh

• Detect: Identify the likely line type (mobile number vs VoIP vs landline).
• Validate: Confirm the number behaves like you think it does (connects, answers, accepts SMS, or bounces).
• Route: Choose the first channel and fallback sequence based on risk and speed-to-connect.
• Refresh: Re-check periodically because number porting and reassignment change outcomes.

In recruiting, line type is not trivia. It’s a workflow control: it determines whether you should call, email, or (carefully) text. The trade-off is… you’ll spend a little time classifying and validating, but you’ll stop burning attempts on the wrong channel.

Step-by-step method

Step 1: Detect the likely line type (fast triage)

Bucket the number as mobile number, VoIP, or landline. You’re aiming for a first-route decision, not certainty.

VoIP (plain language): calls are routed over the internet instead of a cellular network or traditional landline. In recruiting, VoIP often means a business phone system or shared routing, but not always.

Line type definition: the category describing how a phone number is provisioned and typically behaves—mobile (cellular), VoIP (internet-based calling), or landline (traditional fixed-line). In recruiting ops, it’s a proxy for reachability and channel fit.

If your team uses a line type lookup, treat it like a starting point, not a final answer.

Step 2: Validate with behavior (because porting blurs signals)

Detection can be wrong because of number porting and reassignment. Validate using what happens when you actually try to reach the person.

Porting definition: when a phone number is transferred from one provider/service type to another while keeping the same digits. Porting can change whether SMS works, who answers, and how calls route.

Suspect porting or business routing when:

• Detection indicates mobile, but you repeatedly hit an IVR or operator greeting.
• Different attempts produce inconsistent outcomes (personal voicemail one day, front desk the next).
• SMS delivers but responses come from staff or a generic shared inbox.

• Call behavior: personal greeting vs IVR vs generic mailbox.
• Wrong-party signals: staff answers, clinic operator, or “you have the wrong number.”
• SMS behavior: only test SMS when you have consent where required and you include opt-out language.

Step 3: Route outreach based on line type (and risk)

Route your first attempt to maximize connectability and minimize compliance risk:

• Likely mobile number: Call first when urgency is high. SMS is optional when appropriate and you can honor opt-out immediately.
• Likely VoIP: Call and email first. Treat SMS as higher risk until the clinician confirms it’s personal.
• Likely landline: Call during business hours; expect gatekeepers; use email to confirm the best direct contact.

If the line type is unknown after two attempts (one call + one email), stop guessing with SMS and move to confirmation-first outreach.

Step 4: Refresh and suppress

Numbers decay. Build a refresh loop and suppression rules so your team doesn’t keep hammering stale or shared lines.

• Refresh line type when outcomes contradict detection (e.g., “mobile” that always hits an IVR).
• Suppress numbers that generate repeated wrong-party responses or any explicit opt-out.
• Log outcomes by line type so routing improves over time.

Diagnostic Table:

Heartbeat.ai ops note: when you have multiple numbers for the same clinician, prioritize the one most likely to connect first; Heartbeat.ai can support routing with ranked mobile numbers by answer probability.

Weighted Checklist:

Use this to decide whether a number is “safe to text now” vs “call/email first.” Score it, then follow the decision.

• +3 Candidate explicitly provided the number (or confirmed it in writing).
• +2 Detection indicates mobile number.
• +1 Call reaches a personal greeting (not an IVR).
• -2 Detection indicates VoIP or landline.
• -2 Any shared-line indicator (IVR, operator, front desk, group voicemail).
• -3 Any explicit opt-out or wrong-party indicator.

• Score 4+: SMS can be appropriate if you include opt-out language and you have consent where required.
• Score 1–3: Call first, then SMS only after confirmation.
• Score 0 or less: Email/call via office route; do not text until identity and appropriateness are confirmed.

Outreach Templates:

Template 1: Voicemail (mobile-leaning)

Voicemail: “Hi Dr. [Last Name]—this is [Name] with [Org]. I’m calling about a [role] opportunity in [city]. If this is the best number, call me at [number]. If not, email me at [email] and I’ll update my records.”

Template 2: First SMS (only when appropriate)

SMS: “Hi Dr. [Last Name]—[Name] with [Org]. Are you open to a quick call about a [role] option in [city]? Reply YES/NO. To opt out, reply STOP.”

Reminder: Only text when you have consent where required and the line appears personal. Always honor opt-out.

Template 3: Email opener (VoIP/landline-safe)

Subject: “Confirming best contact for [role] in [city]”

Email: “Dr. [Last Name], I’m recruiting for a [role] role in [city]. Can you confirm the best number to reach you directly? If you prefer not to be contacted, tell me and I’ll mark an opt-out.”

Common pitfalls

• Assuming line type is a guarantee: porting and reassignment mean you need outcomes-based validation.
• Texting shared lines: VoIP and office systems can be monitored by staff. Confirm personal ownership before SMS.
• Ignoring opt-out: if someone opts out, suppress immediately across channels and systems.
• Over-dialing the wrong route: if it behaves like a clinic system, stop treating it like a personal mobile and switch to email + office-hour calling.
• Not tagging outcomes: without logging by line type, you can’t coach reps or improve routing rules.

How to improve results

Improvement comes from measuring outcomes by line type and adjusting routing rules. Measure this by… tracking each attempt with (1) detected line type, (2) channel used, (3) outcome, and (4) whether the clinician confirmed the number is personal.

Measurement instructions

• Connect Rate = connected calls / total dials (e.g., per 100 dials).
• Answer Rate = human answers / connected calls (e.g., per 100 connected calls).
• Deliverability Rate = delivered emails / sent emails (e.g., per 100 sent emails).
• Bounce Rate = bounced emails / sent emails (e.g., per 100 sent emails).
• Reply Rate = replies / delivered emails (e.g., per 100 delivered emails).

What to log on every attempt (so you can coach and iterate):

• Detected line type (mobile/VoIP/landline/unknown)
• Channel used (call/email/SMS)
• Outcome (connected, answered, voicemail, IVR, wrong-party, opt-out, reply)
• Next action (retry window, switch channel, suppress, refresh)

Refresh triggers (don’t wait for a quarterly cleanup):

• Detection says mobile but outcomes look like IVR/operator.
• Any wrong-party response.
• Repeated no-connect patterns that contradict the expected line type.

Weekly ops review (simple, repeatable):

• Compare Connect Rate and Answer Rate for numbers detected as mobile vs VoIP vs landline.
• Compare Reply Rate for call-first vs SMS-after-confirmation sequences (only where SMS was appropriate).
• Track wrong-party and opt-out rates by source; refresh and suppress aggressively when they spike.

Uniqueness hook: DECISION_TREE routing worksheet

Use this decision tree to route outreach without overthinking it:

• Step A: Detect line type
  • If mobile number → go to Step B
  • If VoIP or landline → go to Step C
  • If unknown → go to Step D
• Step B: Mobile route
  • Call first
  • If appropriate and permitted: send one SMS with opt-out
  • If no response: email to confirm best contact and preference
• Step C: VoIP/landline route
  • Call during business hours; expect gatekeepers
  • Email to confirm direct contact and preference
  • Only SMS after the clinician confirms it’s their personal number
• Step D: Unknown route
  • One call attempt + one email
  • Classify based on behavior; then follow Step B or C
  • Refresh the record if outcomes conflict

Legal and ethical use

Recruiting outreach needs to be compliant and respectful. Build your workflow around permission, transparency, and fast suppression:

• Consent: a personal number is not automatic permission to text. Get consent where required and keep messages relevant.
• Opt-out: make opting out easy and honor it immediately across systems.
• Minimize exposure: avoid sending sensitive details to numbers that may be shared (common with VoIP and office lines).
• Document your process: keep logs of outreach and opt-out handling.

For baseline guidance on unwanted calls/texts and TCPA context, review the FCC resources linked below.

FCC TCPA overview

Evidence and trust notes

This page is written for recruiting operators. We treat line type as probabilistic because number porting and reassignment are common, and outcomes matter more than labels.

• How we think about data quality, verification, and suppression: Heartbeat trust methodology.
• More provider contact data workflows: provider contact data resources.
• Regulatory baseline for unwanted calls/texts: FCC guidance on stopping unwanted robocalls and texts.
• TCPA overview: FCC TCPA overview.

FAQs

Is a VoIP number always a business line?

No. Some clinicians use VoIP personally, and some practices route calls through VoIP systems. Treat VoIP as a higher shared-line risk until the clinician confirms it’s personal.

Can a mobile number be non-textable?

Yes. Some mobile numbers can’t receive texts due to settings, service issues, or how the number was provisioned after number porting. Validate with outcomes and don’t assume.

What should I do if line type says “mobile” but I keep hitting an IVR?

Assume the number is ported or being routed through a business system. Reclassify it operationally as business-routed and switch to call/email first.

When is it appropriate to send an SMS?

When you have consent where required or a legitimate outreach rationale, the number appears personal, and your message includes clear identification and opt-out handling. If it’s VoIP/landline or shared, confirm first.

How does line type affect recruiter metrics?

It changes your Connect Rate and Answer Rate on calls, and it changes whether SMS is even a reasonable channel. Track outcomes by line type so you can route smarter and reduce wasted attempts.

Next steps

• If you’re standardizing routing across your team, document your rule for how to tell if a number is mobile or VoIP so reps don’t improvise under pressure.
• To align your team on which number to try first (office line vs direct dial vs mobile), see: office line vs direct dial vs mobile: recruiter routing.
• If you need a deeper workflow for confirming whether a clinician number is usable for outreach, use: number usability check for clinician outreach.
• If you want to operationalize this routing inside your sourcing workflow, start free search & preview data.

About the Author

Ben Argeband is the Founder and CEO of Swordfish.ai and Heartbeat.ai. With deep expertise in data and SaaS, he has built two successful platforms trusted by over 50,000 sales and recruitment professionals. Ben’s mission is to help teams find direct contact information for hard-to-reach professionals and decision-makers, providing the shortest route to their next win. Connect with Ben on LinkedIn.