You probably need to talk to your mobile service provider...you may need to compare the capabilities of your device (e.g., radio frequencies) against those which the carrier uses (e.g., if they do or do not natively support your specific BB model number).
Occam's Razor nearly always applies when troubleshooting technology issues!
If anyone has been helpful to you, please show your appreciation by clicking the button inside of their post. Please click here and read, along with the threads to which it links, for helpful information to guide you as you proceed. I always recommend that you treat your BlackBerry like any other computing device, including using a regular backup schedule...click here for an article with instructions.