tc35i factory settings for bounrate is 2400 not 9600!
Becouse you use max its not inverted signal.
on 2400 and true settings should be 396 if you use 4mhz crystal.
here example of code how to star communication with modem if max232 is used:
Code:
 Init:
serout tx,0,["AT",13]
serin2 rx,396,1000,init,[WAIT("OK")]