My wife and I have the same problem with Siri. In our contacts database, each person has at least one associated phone number (usually associated with 'home', 'mobile' or 'iPhone'). However, even though these numbers are the typical 10 digits used in N. America, Siri frequently will be unable to dial the number despite finding the contact and the number in the database. Question: can this be fixed without re-entering the numbers to the contacts database? What causes some 10 digit numbers (and numbers with the +1 in front of them) to be unrecognizable for purposes of making Siri-initiated phone calls?
Believe it or not, this is often a minor activation issue–assuming the iPhone is on Sprint or Verizon. On Verizon, Dial *228 from the Phone app. On Sprint, dial ##UPDATE# (##873283#). Follow the voice prompts, if any. The process takes a minute or two. After you get a pop-up message indicating the update was successful, wait another minute. You should see your service indicator go away for a moment then come back.
Afterward, try Siri again. This will likely resolve your text message issues too, though a restart of the iPhone (hold sleep/wake button, swipe to shut off, wait, start back up) may be necessary there.