SMS Bounced Messages and Twilio
With regard to SMS messages bouncing due to the contact number not able receive SMS messages or possibly an old phone number, it will NOT affect your credibility with Twilio in account. That means that if you send DR out to old contacts and for whatever reason they provide a number that is either old or perhaps a landline, you will not be penalized. This should relieve you of any stress about sending out DR to a client's database that may be a little old.
HOWEVER
Twilio has specifically stated they do NOT want their platform used for cold SMS marketing messages regardless of any laws (or lack thereof) for B2B sms marketing. This means Opt-in techniques will need to be used BEFORE sending. (TBD) Twilio may BAN your account for doing cold SMS marketing and you risk pass through fines by Major Carriers such as AT&T by as much as $10,000 for SPAM complaints and $1000 for "snowshoeing." Snowshoeing is sending similar messages from different numbers. You've been warned.***