clock iPhone 4 is getting behind

My system clock of my iPhone 4 is getting behind. It's set to automatically and I know it could be my telecom provider.

Though, I reset my iPhone this weekend and the time was for one day in exact sync with all the other clocks (my Mac, and other timesyncclocks). But now it's five seconds behind, after a few days. My girl friends iPhone 3G is still always on time, after two years... How is this possible?

It's way too bad. My clock is getting behind a second every day, and syncing with T-Mobile does only work when do a restore of the phone...