Thanks, mister_e!

Actually, I just want to use a PIC to communicate to one single I2C device. I won't have any external serial communication via a computer or something similar.

I wanted to make my circuit very small, so I wanted to get rid of any components that are not too crucial. My main concern is that if I don't use a crystal then I wouldn't be able to communicate accurately with the I2C device.

But that is good to hear that you haven't had any problems using the internal oscillator with the I2C device.