I asked that question because I am testing the internal oscillator with a frequency meter. A simple routine switch a pin on and off... the pin turns on and off @ 50 Hz, if a crystal is used. When using the int osc the frequency is 58 Hz without calibration and it becomes 52 Hz with calibration.
What do you think of theese results in order to make a serial communication (@2400 baud)?
As I said before, the internal oscillator is fine for serial, certainly as high as 9600 baud which I always use - so 2400 baud is even easier!. This is on a 16F628, where there is no calibration adjustment, so a calibrated PIC should be even better.