We use a Sunrise SunSet ISDN hand-held unit for day to day use, works great for T-1 & ISDN but I think they are discontinued or out of business now, it had been around here a long time when I started about 4 years ago.
We borrow the CO's T-Berd on occasion, not sure the model but it is a tablet like device, works amazingly well but I think they said it was around $8000!
One of the ILECs here that does a lot of PRIs uses Argos PRI testers, they seem to work really well too.