A lot of cell phones have the same IP when running off of 3G. If a member got IP banned using their phone and they had the same IP as you, that's probably why. Phone IPs change all the time, though, so you should be unbanned soon.
This is one method, as well as also manually selecting another carrier and then yours. That's the way I do it, as it renews it, and it can be done quickly without losing all the other signals.