Thanks everyone for your feedback - its very useful.
I perhaps confused matters by asking two questions in one.
My first was around the issue of hotdesking using two differing models of phones - 5212 and 5224's and the problems with the different button mappings.
The second question was related to issue above - I am in the process of evaluating the UCA ver 3.2 and was wondering if anyone had rolled this solution out, if so if people could give me an idea of how the roll out went in terms of issues, cost and user perception.
Thanks again everyone who has replied.