Dear zulkifli,
I suggest that you get familiar with working with the TC35i modem connected to your PC serial port using the Hyper Terminal software with "AT" commands before you connect the TC35i to the uC. The Hyper Terminal configuration needs to be set with the correct port number (example Com1), Baudrate (example 9600 bits per second), Data bits (8), Parity (None), stop bit (1) and flow control (example none). If the setting is correct, type "AT" and Enter on the Hyper Terminal and the TC35i should response an "OK" on the screen.
Look into the rest of the ETSI AT commands of the TC35i to be familiar with how it works and try to duplicate the sequence of AT commands using the uC with the same baud rate you are using with the Hyper Terminal. Use a MAX232 chip between the uC and the TC35Ci serial port to translate the 0-5V of the uC to +12-12v signal required by the TC35i. Use PICBASIC or any convenient software to program the uC in sending AT commands. Correct signal frequency and polarity are key to successful connection.
Good luck.