That would arguably make it a "wireless telephone", but no mere functional change could make it a "handset".
Hmm, not sure
(Google)define: handset
•The part of a telephone, containing both receiver and transmitter (and sometimes dial), that is held in the hand
http://www.google.co.uk/search?hl=en&source=hp&biw=1276&bih=815&q=define%3A+handset&aq=f&aqi=g10&aql=&oq=&safe=vss
The iPad 2 has both a speaker and a microphone on a single unit - it contains both a receiver and transmitter so does that not make it a handset?