Apple – Support – Discussions – address book smart groups ….  Joaisey has a nice Applescript that does this.  Great work!  This is a huge help for anyone who has Facetime.

– Add iPhone Tag –
– John Maisey – www.nhoj.co.uk – 7 Dec 2010 – v1
tell application “Address Book”
set myPeople to people whose label of phones contains “iPhone”
repeat with thisPerson in myPeople
set myNote to note of thisPerson
if myNote is equal to missing value then
set myNote to “has_iphone”
else if myNote does not contain “has_iphone” then
set note of thisPerson to note of thisPerson & return & “has_iphone”
end if
end repeat
save
end tell