I have a Siemens TC35. I can send message with hyper terminal. Also i have a easypic4 and i can connect with hyper terminal.
If i can connect the easypic4 with Siemens TC35 and use the bellow coce never the led on portb.6 go on

DEFINE OSC 8
DEFINE HSER_TXSTA 20h
DEFINE HSER_RCSTA 90h
DEFINE HSER_BAUD 9600
DEFINE HSER_CLROERR 1

SMS:

HSEROUT ["AT" ,13,10] ' send AT to modem followed by a CR and line feed

HSERIN 5000, SMS, [WAIT("OK")] ' now wait for 5secs until OK is received however
' if it is not then goto the SMS routine again

HIGH PORTB.6 ' don't go on
pause 1000
LOW PORTB.6

end