What do you have set as outbound caller id in the extension? Did you copy them and perhaps all have the same setting there? Do you set the outbound caller id in the outbound route perhaps? It should be something like effective_caller_id_number=${outbound_caller_id_number} and not effective_caller_id_number=all_the_same_number. If everything seems OK, maybe the provider is changing the outbound caller id? Check if the invites being sent have different caller_ids.
