If your missed-call system texts every caller, some of those callers are on landlines. The message gets accepted, your logs record a success, and nothing reaches the customer.
Accepted is not delivered
A successful response usually means the message was accepted for delivery, not that a phone displayed it. Send to a landline and it depends on the carrier: some read the text aloud, many simply discard it, and a few report the failure late, after your system already logged a success.
Who still calls from landlines
Property managers, a receptionist booking a commercial repair, an older homeowner who's kept the same number for decades, a clinic front desk. Often the callers worth the most. Nobody has measured a reliable percentage, so check every number.
The fix: check before you send
A carrier lookup service (Twilio Lookup is the common option) returns the line type for under a cent per number. Check current pricing. Then route on the answer:
Mobile: send the text.
Landline: don't text. Alert a person to call back straight away.
VoIP: try the text, and alert a person if delivery fails.
Check at send time, not once. Numbers get ported between carriers and line types, so a saved result is a guess.
Why not auto-dial them back?
An automated recorded call sits in a different regulatory category than replying by text to someone who just contacted you, so get real advice first. Start with flag-and-escalate and decide with real data.
Watch for silent success
The failures that last longest are the ones that report success. Make sure at least one alert fires on something missing, not just an error.
Full article: https://www.stephenthorn.com/blog/texting-a-landline-silent-failure/