Just a few weeks ago at my great uncle's funeral mass a woman's phone rang during the eulogy. She answered the call, but got up to walk to the back of the church, so she was doubly disruptive. The worst part is that she didn't leave the church, she stood in the back and talked. It was a very old church and the sound really carried. Everyone could hear her conversation and you could see how uncomfortable everyone was.
Also, my sister's phone rang as they were carrying the casket from the hearse into the vestibule. Everyone was totally silent at that point. She tried to turn it off quickly, but we all caught a couple of verses of "Come Theodora, don't spit on the floor-a" or whatever that stupid song is (that's the tune her cell phone plays). After that, I couldn't stop laughing (but that's another thread!)