I orriginally assumed this was a game bug, but I haven't seen anyone else report the same issue, so I take it must be something I've done.
When I direct my sims to use their cellphone, it evaporates and becomes stuck. If it rings and they pick it up, autonomusly or by direction, it works. As soon as I tell them to call someone, it disappears and I get a jump and this error:
Normal phones work.
I did remove my hacks folder before installing Pets (but I can't entirely guarantee that there isn't something hiding in some other folder), and I have as far as I can tell only added the director's (updated today) cut and som awesome hacks by twojeffs (confirmed ones).
I've never been good at interpreting error logs, so I'm attaching it in the hope that someone more awesome than me can tell me what I've done wrong.