Exup,
I started off with just the headphone/mike setup from Maplin's which costs approx the 25 quid I said. Sound quality was good upto 70 or so. But as I wanted some music as well I upgraded to the intercom system from Maplin's which costs about 80 quid. This gave me a much better sound quality, also I could have other inputs such as an mp3 player.
I use the Ipaq in my tank bag, which means that I can have a quick look if necessary, but I've found the voice instructions good enough so far
The intercom plugs into the headphone socket on the Ipaq, and is straight forwards. One point to note if you use the BT reciever under the seat, is that it maybe necessary to put this into a poly bag!!!
As I'm an electronics tech I've used good quality quick disconnect connectors everywhere.
Any more questions then give me a shout
Neil