T1's cell phone went off recently when I was on the phone with her (she has a land line that I call). It was strange because all of the sudden I heard crickets chirping and was like, "Wait...where are you? it sounds like you are outside but I am talking to you on your landline so I know that's not possible" and she laughed and said she was sorry, that it was her cell phone ringing. That particular session was on a Friday, it was a second session for me that week and she doesn't normally meet with clients on Fridays so she hadn't turned her phone ringer off. That made sense. but I wouldn't like that if it happened regularly.
T2's phone rings sometimes but it is in another room so it is not too distracting.
In the beginning of this thread some people mentioned that their Ts read text messages or even answer their phone during a session. That would be grounds for firing them as a T as far as I'm concerned. They can check their texts and voicemails in between sessions. In the extreme situation where they might need to take a phone call from a suicidal client, I would be understanding but to sit there and read texts from other clients during a session is very unprofessional.