Mack. Contrary to anyone saying you don't need a PTT switch and in addition to most other people saying you do, can I just stress that you MUST get a PTT switch for the reasons given by Maxx2.
VOX is NOT an alternative to the PTT switch.
In addition to the anecdotal evidence suggested above I too have experienced someone using Bike to Bike radio WITHOUT PTT.
It was aj in Germany who thought it hilarious to broadcast continually his singing to other bikes riding with him. This had been mentioned several times in the past and the fact that he really needed a PTT switch. Said he didn't need one. Reasons why one was needed were suggested, but fell on "deaf ears" and the advice declined. Then, on one particular ride, within a few minutes of getting underway, the open broadcast singing to "yasself" started
.. After a minute or two of laffing about it, the next 20 minutes became interminable ( one mans humour is another mans whatever and all that)...until finally, out of sheer frustration and anger at some coont spoiling your ride, a pull over to rip the lead from ya helmet was required, thus preventing me from listening to MY music and MY Garmin and also speaking to any other riders with PMR's.
.
Fortunately I have never experienced this since..
So, Poacher, go get a PTT switch for starters. On the PTT switch you have 3 positions, one for it to be disabled, another for it to be "open linked" so that whenever you talk the VOX automatically kicks in and lets you broadcast and finally the middle positon which is what it says on the tin i.e. press to talk.
Let us know how you get on.