Sometimes you need to use a "toll free" area code as high volumes of messages can get you blocked by carriers if you exceed a certain volume threshold. They generally have a higher tolerance... or split it up with multiple numbers... sometimes changing a number is just a necessity.
Took us a while to figure out how that all worked and how to split the volume over different channels. Probably not an issue for a single SP, but groups, agencies, collectives etc... don't freak out when numbers change or if the area code is different than you expect.