I have bluetooth connectivity with my LightSpeed Zulu to my phone, but don't turn on the bluetooth in the air. I don't want someone distracting me while on short final... However it would be available in the event of a problem.
Now buying headsets.... that's a different thread topic talked about many times before!
As said below - mobile phone is only as good as the reception it has. No good in the middle of nowhere and variable reception over towns above 1500 feet (some people seem fine up to much higher, others don't). But a hand held with its internal aerial wont have a huge range either - but it would be enough to contact a commercial jet going overhead at 20 000 Feet who could relay a message.
But as Backpacker says - its almost certainly not required at the moment. Talk to your instructor about what they would recommend.