Yes, Avaya has analog cards.... Avaya has the best phone features and call center features. In the regular office space, many such as Shoretel and Cisco compare the same as Avaya. If you implement Avaya VOIP correctly and your network is robust, it rocks.... Support wise, Avaya scored better than the rest as well... I rarely call them (I get way more help from this forum than I ever have from Avaya) but when I do, it's always a pain with complex out of the ordinary issues. They are expensive.... as well.
My Opinion..... And from information that I've read in various market research articles/white papers….. Avaya is the way to go.
As far as converting goes.... in the Avaya space if you have TDM it's not worth it to rip it out and replace with VOIP. In the end you still have dial tone at the desk. Going forward with new installs.... yes VOIP all the way. The environments can be mixed as well. Again.. my opinion..
Thanks,
Wildcard