Problem with Blackberry Curve 9300?

So, every now again well a few times a day shall I say. My blackberry stops receiving bbm messages, and stops status updates on bbm. It can last around 20 mins or so?? I noticed this problem on saturday. I'm on pay as you go network t-mobile.. I've never had the problem before. Is there anything I can do to fix this? It's really starting to bug me now