Several users on the Google support forums have been reporting for long about a bug that has been causing the stock messaging app on the Android handsets to malfunction. Some users have experienced this inability to send SMS after they upgraded to the new Android 2.2 while others have seen the same bug on the older Android versions as well. Also, for some users it appears to be a case solely with the stock messaging apps since other third party SMS apps like Handcent seem to be working flawlessly. It is being observed that a good number of users have been using pretty old SIM cards.
While there is no official fix to the issue as yet, one member has come up with some sort of a fix that appears to be working for a lot of users,
“For anyone else with this issue heres how i fixed it (on my own w/o T-Mobile’s/Google’s help)
Open the dialer in and type in
Scroll all the way down on the page that opens and type in your smsc number.
T-Mobile’s SMCS is +12063130004
Use at your own risk!”
Now, do note that the SMSC number changes for every operator. To know the SMSC of your carrier, you may want to call up customer care and ask about it.