Hey there folks! I just finished flashing my At&t Xperia X10a over to 2.1 and I must say it does move a lot quicker now. Big problem, however, is that I cannot get it to re connect to the network. When I boot up the phone it will tell me to choose the language. When I select English(United States) it then pops up with "Please insert SIM card and restart your phone." I can hit Cancel and get into the phone and still use everything. Wifi works and all the apps are working no problemo. I just cannot connect to the cellular network at all. Steps I've taken so far are to go into the settings to Mobile Networks and go to network operators. When you enter, it Searches for mobile networks and locates At&t (and while i'm writing this, for the first time T-Mobile as well -not important). When I Select At&t it says "Registering on At&t" then it fails saying "Your SIM card does not allow a connection to this network." I know the SIM card works cause I have another phone that i've put it into without any issue. Conversely I've taken my iPhone 3gs SIM and put it into the Xperia just to try to get it to connect and its the same story with the SIM card does not allow a connection to this network. I'm super stumped here and would appreciate any help.