I've had the same problem since I've had this horrible phone. Here's how to fix it:
If those 2 steps still don't work then you have to turn it off and turn it back on. I always just do the cache first otherwise if I do the cookies I have to re-enter all of my online passwords (Facebook, Yahoo, etc. )
Hope this helps!
I Have the same phone also and i don't have that message popup anymore because i am a phone expert...
2.Click App Settings
3.Click Access Points
4.Click New Profile
5.Name Access Point name to T-Mobile Internet (or Network1 As My setting)
6.Scroll Down To Apn And The address is epc.tmobile.com or internet2.voicestream.com
7.You Can Add Authocation settings if you want (i rocommend it)
9.return back to the operator Menu
11.scroll to Internet Profiles
12.Add new One
13.Name it to T-mobile Internet1 (or network2 as my setting)
14.if you want to use proxy settings turn it on and input 10.177.0.34 or (10.168.191.166 currently using this setting) for the proxy web address ...and port number is 80...
15.acess point name is T-mobile internet Or (Network1 As My setting)
17.go to browser account and Name It Network2 Or T-mobile internet
18.webpage should be http://wap.tzones.com or use www.google.com or any other website you log on to first
any other information contact me at firstname.lastname@example.org