I am having the same issues too. Will have data for a couple of days and then nothing. I tried the airplane mode and that does not work. I have to do a hard reset on the phone for it to come back on. At first I thought I just had a timer on that I didnt know about. But it looks like its a common problem.
Not that I believe it's a valid solution to the real problem, but you can probably achieve the same result by turning on airplane mode, then turning it back off and that will bring your connection back.
Following. I've had my phone for five days and today it kept losing data. It would show 3G in white with two bars, which means my signal sucks and it wouldn't do anything data related.
I turned it off/on and now I have blue 3G with all bars and all my data is synchronizing again. I can't believe such a major issue exists on a $300 device.