This is a quote from a nairalander
I have an issue that's driving me nuts. after
updating bbm & getting it active using my office
wireless, everything worked like magic both on
wireless & mobile network.
The problem now is once I restart my phone while
using it on mobile network, BBM stops working
while every other app that needs data connection
keeps working like normal. I can neither send nor
receive bbm messages but as soon as I enable
wireless connection in d office, BBM starts working
until the next restart on mobile network.
I've uninstalled & reinstalled d app to avail. This
didn't use to happen with the older version. Any
ideas on what the problem could be?

I use to have this problem also with my bbm but I decided to change my apn to blackberry.net instead of the web.gprs.mtnnigeria.net and then remove the proxy and port, save and then you are good to go.