Can't log into google apps after sim card change
First, I'd start by ensuring that the APN settings are correct.  A different SIM card from another carrier could have overwritten them.  You can access these by going to Menu -&gt; Settings -&gt; Wireless &amp; networks -&gt; Mobile networks -&gt; Access Point Names and then tapping on the selected one to edit it.  The correct settings are sometimes listed on your carrier's website.  At worst you may need to call their support line.  While you are there, make sure under "Network Operators" option your provider is selected.  After making the changes toggle the Airplane mode on and off to re-connect to the mobile network.

Try dialing the following number in the Dialer app: *#*#2432546#*#* (spells out "checkin" between the stars and pounds) and see what it comes back with.