int c = serialgps.read();
My guess is that the serialgps buffer does not contain a complete GPS statement. I recommend you put the gathering of the GPS coordinates OUTSIDE the sending of the SMS. That way you can have the coordinates immediately available.
Note: You should probably check that the TinyGPS library has received a valid fix (if (gps.location.isValid())) before asking it for the coordinates. You don't want to replace good coordinates with bad coordinates.