1. Check Blackberry Internet Service (BIS) Web Interface to make sure account is still active and doesn't need to be re-validated:
   • AT&T/Cingular: https://bis.na.blackberry.com/html?brand=mycingular
   • Verizon: https://bis.na.blackberry.com/html?brand=vzw
   • Sprint: https://bis.na.blackberry.com/html?brand=sprint
   • T-Mobile: https://my.t-mobile.com/Login/
2. Re-Send Service Books to Blackberry device from BIS Web Interface
3. Re-register Blackberry device:
   
   
   • AT&T Blackberry Bold 9000:
   
   
4. Check data connection on Blackberry device - attempt to browse to a web site to see if it works
5. Make sure the Blackberry device has a strong signal in the current area
6. Reboot Blackberry device: remove battery (and SIM Card if applicable) from Blackberry device and keep out for 30 seconds - 1 minute before re-inserting and powering Blackberry device back on
7. Check to see if it is an issue with the email provider or Blackberry/cell provider (maybe see if the email provider is experiencing any difficulties, or if other people who use the email provider are still able to get email on their mobile device (most specifically on Blackberry, but knowing about iPhone, Exchange ActiveSync, etc. might help also))
   • maybe contact email provider to see if they are experiencing any issues (and more specifically - any issues with Blackberry devices or services)
   • maybe contact Blackberry/Research in Motion (RIM) to check if they outages or other problems that might be causing issue
8. Final Attempt at Resolution - (DO NOT Attempt this until you have exhausted all other options as it will delete all saved email off of the Blackberry device) : Delete email account off of BIS Web Interface and then re-add email account back on to BIS Web Interface (first be sure to note all details of email account)

For further support, please see the following website: http://na.blackberry.com/eng/support/software/internet.jsp