gorgon:
...like "SR125", then split that message into "SR1" (meaning servo 1) and then the value "25". I get the "SR1" message filtered out just fine, it converts to string, but getting the number part from the char* seems more tricky..
As Paul says, atoi() is your friend.
You might want to think about splitting your message on the 'SR' then convert the '1' into an integer, which you might use as an index into an array of servos.
Also. Read your code again. You enter the IF conditional when size is > 0 but then proceed to always reading a message of more than one byte. Is that what you mean to do?