UPDATE : The issue has been fixed in the latest update released. Launch Cydia and update GV Mobile to v1.22.2 and you should be all set!
Sean Kovacs’ GV Mobile is no doubt the best native iPhone client available only on Cydia after Apple’s asinine decision to block all Google Voice related apps from the AppStore.
GV Mobile App suffered from some issues after Google Voice changes on the web front end. The two known issues being :
Invalid Credentials Error
Login Info not being saved (requiring username/password each time the app was launched)