It’s likely that you need to update the operating system for it to be more compatible/current with your carrier’s network and protocols. As Iphone35 mentions above, a call to them will enable you to do this, as they should be able to flash update your phone with the latest system resources (called service packs in the Bb lingo if I remember correctly), which should rectify the issue. I had a Crackberry prior to the release of the iPhone and remember the same kinds of issues happening once in a while.