46xx and 56xx Avaya IP phones were supported on 406v2 until R3.2
With R4.0 Avaya only supported new style 46xx Phones, and 56xx, however I did have one site on R5 that still had a 4624 IP phone in their stockroom without issues.
On R4.2 and up 1608, and 1616 IP Phones ( first series ) are supported, 1603 on R5+
All the above Avaya IP Phones only interact via H323 on IP office.
You do not need licences to use Avaya IP phones, unless You are on R6+
As for H323 trunks, back in the Day there was AGN buisness class VOIP, they did a great job with H323 service, and support for IP Office. They are no longer in buisness.
I beleive LES.net still supports H323 trunks.
If memory serves Me right SIP licences consumed for H323 trunks, so Yes, you will need SIp turnk licence. It's been a while since I have delt with H323 trunks, so I could be wrong.
Andre