I've been asked by a national service provider to program a 9508. I'm assuming that it is on an IPO. Is there anything in particular that I'll need to know or have (other than someone to guide me) in order to do this?

A 9508 is a digital phone with 24-programmable keys. If you know how to program the IPO in regards to putting a phone into a group, assigning features/keys, etc (or know someone who does), the 9508 is no different than any other digital phone in that respect.

You'll need the Avaya IP Office Manager software to program the phone. There is very little you can do without it.

All above are correct. If current 9.1 release, you can use web administration as well.

when do you have to go onsite?

False alarm. As typical with nationals, they found someone else who could get there faster. Thanks for offering to assist, fellas!