You'll be wanting to run your pic at 20MHz to stand a chance of your phone system
recognizing the DTMF tones produced by PicBasic/Pro.
Don't forget to DEFINE OSC 20
The tones produced by the pic aren't a very pure sine wave.

An external DTMF generator chip would be best,
but I have used a 16F84 to dial numbers and navigate DTMF phone menu systems.
One project was an automated thing to retrieve my bank balance over the phone on payday.