I got a set from amazon last year for my mate and I to go euro-touring. They are made by BT, are fairly cheap and are of great quality. The distance between bikes is over 1k in a line (hills and bends is shorter, but if you can see the bike, the intrcom will work). The intercom works with the other intercom, my phone and my Zumo all at the same time. They cut in and out as I choose, with the sat-nav taking auto priority. I can hear fine with earplugs in my ears, the music goes louder than I would want and the battery life is silly good. I have not charged it for weeks. I did a full review on amazon for the product as I was so impressed. At around £80 a pair, there a bargain. Someone on amazon messaged me the other day to ask a question about them and I think they were on sale for £56 a pair!!!
Hope this helps