[SOLVED]Hardware Serial with internal 8Mhz?

I’d like to know, is it possible to use hardware serial with 8Mhz internal clock, or is the error rate in internal clock just too much?

I’ve tried interfacing SIM900 module with the lowest baud of 1200, with and without delaying the Serial input.
I can only receive gibberish that has some parts readable:

­CªÔÔj
AT+CªÔÔj
¡iI: b1C¡HOK
AT¥I?
¡HhIé 0,LC¡HOK
áAT¥Iý

All of those “AT” characters are correct message. The rest is corrupted.

Is the internal too inaccurate, or can I change the Hardwareserial.h/Hardwareserial.cpp settings for 8Mhz clock?
I mainly want to do this to shave off power consumption. I could deal with external 8Mhz or 1Mhz crystal, if that is possible.

Thanks!

EDIT: Here’s excellent calculator to match specific crystal frequency with Serial baud rates:
http://www.wormfood.net/avrbaudcalc.php

Slowest baud rate is maybe not the best to reduce errors try differing rates and see if you get a good match. I use a couple of ATmega8 chips on internal 8MHz at 9600 without problem.