If you send to many messages and exceed the fair use policy of your carrier they may block your SIM card.
You will generally see this as an issue with messages staying "pending" in your conversation streams.
If this happens you have a couple of options:
1 - Purchase a New SIM
This is the easiest option as you can setup a new SIM and be back up and running very quickly.
The downside to this is that any leads that have received SMS from the previous number will no longer be able to reply.
2 - Call and try to get your SIM Reactivated
You can call your service provider and ask why your card is not working anymore.
Since you will normally end up with a level 1 call centre operator they will probably not know why and you may be able to get it reactivated.
If they can see that there has been unusual activity on the account you can take the approach of "playing dumb" and not kniowijg what has happened.
Or as one of our clients did blamed there kid for putting an app on their phone that caused a mass text blast.
Ultimately they will decide whether or not your number will be reinstated.
Use the myCRMSIM Snapshot
If you are doing mass text blasts ensure that you use drip mode and the myCRMSIM Snapshot provided in our support centre