Originally Posted by
opushomes
The problem may be that your phone does not automatically set the APN for the service that you are connecting to. Often with older phones, one must actually manually set it for each carrier. Voice does not use an access point so works as does wifi in every country I have visited. Unlocked phones with local SIM often require the same APN input.
Actually had it happen here in the U.S. when I hooked up my LG AT&T phone on the T-mobile US network after porting over the number and cancelling ATT. Had T-mobile manually set APN and it has worked splendedly since.
The scenario you describe sounds like your phone didn't auto-provision when you changed SIM cards. But that's different from roaming, in which you shouldn't have to change APN (or SMSC) at all. If you do, then something is misconfigured at the roaming partner.