on the 403 you don't need license keys for IP phones, but TBH it is not blessed with a lot of features compared to the new systems.
I would go minimum with an IP406V2 and upgrade to R5.0 as that at least gives you SIP capability for extensions and trunks, 4.2 gives you SIP trunks and both you don't need licenses for IP sets but the VCM channels are a must for any Avaya IP Office.
Is there any reason for IP sets other than going with the trend?
If not stay with your digital sets, they boot in seconds, your network can go down and they still work even though networks go down much less these days it still is a concern.
Joe W.
FHandw, ACSS (SME)
"This is the end of the world, make sure to buy your T-shirt before it is too late"
Original expression of my daughter