GSM Shield testing.
status=READY
OK
AT+CGATT?
+CGATT: 1
OK
AT+SAPBR=3,1,"CONTYPE","GPRS"
OK
AT+SAPBR=3,1,"APN","http.globe.com.ph"
OK
AT+SAPBR=1,1
OK
AT+HTTPINIT
OK
AT+HTTPPARA="URL","http://trence-enterprJ
ERROR
If the modem responds with "OK", there is NOT an error. The modem accepted the command, parsed it, understood it, and executed it.
If the result of that was that it does not appear that gps.php was executed, you need to look at the logs on the server (the one hosting mywebsite.com), and see whether the server even got the request, and what it thought of it, if it did.