With Symbian-based phones incoming messages may be unaccessible for SmsRc (a situation of NOKIA 6600);
some of these phones don't support SMS AT commands at all.
However, there is a solution for this problem. piAccess Link is a third-party software that may be installed on a Symbian-based phone to make it support SMS commands.
PiAccess Link currently enables PC applications to receive, read and delete incoming messages, but not to send outgoing ones. It doesn't yet support Nokia phones. However, all these things are coming soon, according to the authors of piAccess Link. Check the product page to see whether this software fits your device.