Make sure your APN Setting is current: (eg. vodafone australia as below)
Contract
Profile name: VF Mobile Broadband
APN: static & "vfinternet.au"
Authentication Access Number: *99#
Username: [left blank]
Password: [left blank]
Prepaid
Profile name: VF Prepaid Mobile Broadband
APN: static & "vfprepaymbb"
Authentication Access Number: *99#
Username: [left blank]
Password: [left blank]
http://www.vodafone.com.au/personal/mobile-broadband...