History now but I looked this up out of curiosity. It seems the change come in R6.0 looking at TB115:
Avaya IP Telephone licensing: IP500 and IP500v2 ONLY
In IP Office Release 6.0 all Avaya IP telephones will need to be licensed (this
includes desktop phones like 5600, 1600 or 9600 IP phones as well as wireless
phones like 3600 and 3700 series). Digital phones will not be licensed. This applies
to IP500 and IP500v2 only. IP406v2 and IP412 systems will not require IP Telephone
licenses for Avaya IP Phones.
Removal of VCM channel licenses: In order to reduce product complexity, all VCM
licenses will also be removed. VCM 32 and VCM 64 cards will always deliver 32 and
64 channels respectively (subject to existing codec restrictions). Each VCM 32 and
VCM 64 card comes with 12 Avaya IP endpoint licenses enabled. Once the system is
upgraded the license will show in the IP Office configuration as a “VCM Channel
Migration License”.
Note: The Combination card does not come with any Avaya IP endpoint licenses.[/i]