We have two different recent threads asking if you are allowed to place your phone number in your Google ads. The two threads are at Google Groups and WebmasterWorld and in both threads, a Google representative came in to say, yes it is allowed.
For example, a search on new york dentist has an ad with a phone number in it:
Google said, "Yes, you may use telephone numbers in AdWords text ads. It is not against AdWords policy."
But does Google recommend it? It depends, for some advertisers it works well, Google said. But for others it doesn't work well - people still want to "click and learn," Google said. Google recommends doing a simple A/B test, "with two ads in the same ad group - one having the phone number, and the other without."
Testing to see what works best for you is a great idea.