The oscillators are close when they come from the factory, but I need 100% reliable communication at 19.2K baud, over the temperature range of -45 to 100C when running from a 4Mhz internal oscillator, and the supply voltage varying between 4.7 and 5.1V.

Now you see why I'm interested in frequency stability and calibration!

Amazingly, the 18F2221's (without calibration) are *usually* good enough to get this done.