When an SMS Bounces, Iterable sends you back an error code in the event payload. This error code in particular means you've likely attempted to text a landline or a non-cell phone.

https://www.twilio.com/docs/api/errors/21614

If you aren't looking to pay for a service to assist you with checking if a Phone Number is a mobile number, you can build a segment using SMS Bounces.

Build a segment where contact has an SMS Bounce error code is 21614 and doesn't have an SMS reply message of "STOP or UNSTOP".

While this is a reactionary item, it may be valuable when trying to suppress bad numbers from your text campaigns which may help lower your costs! You can also update contact preferences to call instead of text if these are landlines. Or use the list to reach out via email or by phone for an updated mobile number.