If I were doing it, I'd certainly run Cat5 even for phone. It's not much more money and much wiser to install for the future.
But, the question was how to terminate it. Since you've already prefaced it with ATT, the 568B may be the better option depending on which phone it is. If you terminate the wiring on 568B jacks, you should be able to plug ANY phone into it (even those damn old Merlins).
Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com