SEND TEXT file with serial port

AT Returns a "OK" to confirm that modem is working
AT+CPIN="xxxx" To enter the PIN for your SIM ( if enabled )
AT+CREG? A "0,1" reply confirms your modem is connected to GSM network
AT+CSQ Indicates the signal strength, 31.99 is maximum.

4. Sending SMS using AT commands

We suggest try sending a few SMS using the Control Tool above to make sure your GSM modem can send SMS before proceeding. Let's look at the AT commands involved ..

AT+CMGF=1 To format SMS as a TEXT message
AT+CSCA="+xxxxx" Set your SMS center's number. Check with your provider.

To send a SMS, the AT command to use is AT+CMGS ..

AT+CMGS="+yyyyy" <Enter>
> Your SMS text message here <Ctrl-Z>

You send it one byte at a time!

What modem? Who said anything about a modem??

"4. Sending SMS using AT commands"

SMS? Who said anything about sending SMS?

If you want to send a file from your computer to your microcontroller, use for example the HyperTerminal....then select transfer-->send text file
This will send the file character by character.
You can send any file, I use this to send my *.hex file when using a bootloader.

In the configuration menu, inside ANSI options you can set the delay between characters and between new line.
(Usefull when you send a big file and the buffer in the microcontroller is small)

The OP didn't say which direction the "file" was to be sent!

I guess there must be at least a 50% chance that he wanted to send it from the PC to the microcontroller...

In that case, it'd be easier to just do:

COPY file COM1:

"You can send any file"

It would not be a good idea to send anything other than a text file this way...