Rufinus,
I hate to say that, but you have got to do some homework.

Make yourself familiar with the principles of serial communitation and the datasheet of a MAX232.

Pay special attention on the MODES, (TRUE/INVERTED)

If you receiver is expecting the data line to be ILDE HIGH and your transmitter IDLES LOW, (and vice versa) you will see all kinds of strange phenomenon.

You are not really connecting one of the RS232 Outputs of the MAX to the phone or PIC, are you?
(you are about to kill the PIC and/or the Mobile)