Phone number types

What mobile, landline, VoIP, unknown, and toll-free classifications mean for SMS deliverability and calling.

Updated 2 min readMaintained by Landing Zone

A phone number's type decides how you can reach it: mobile numbers can receive texts, landlines generally cannot, and everything in between deserves a closer look. Landing Zone's phone verification classifies each number so you can choose the right channel per contact.

How it works

Verification assigns each number one of four classifications, plus the carrier that serves it:

  • MOBILE — a wireless number. It can receive SMS and calls, making it the primary target for texting.
  • LANDLINE — a fixed line. It can take calls, but texts to landlines generally fail — sending SMS to a landline usually wastes the message.
  • VOIP — a number served over the internet rather than a traditional carrier network. VoIP numbers can typically take calls, but SMS behavior varies by service, so treat them with more caution than a mobile number.
  • UNKNOWN — the line type could not be determined. Verify again later or treat the number as unproven for texting.

Toll-free numbers are a separate category you will meet on the sending side: business numbers (such as 8xx prefixes) that require their own verification process before messaging at scale. See the toll-free verification guide.

Line type feeds directly into sending decisions. The SMS eligibility pipeline considers line type when building a batch, and when a batch contains numbers whose line type has not been verified, Landing Zone asks you to confirm with a "Send to unverified numbers?" dialog — your acceptance is timestamped.

When to use it

Check line types whenever you plan channel strategy: text the mobiles, call the landlines, and verify the unknowns before spending on either. The verify phone numbers guide shows how to run verification in the app.

Limitations

  • A classification is a snapshot. Numbers get ported between carriers and services, which is why verification results are cached for 30 days rather than kept forever.
  • Line type is about deliverability, not permission. A mobile classification does not mean the person consented to hear from you — see Consent records.