I was wondering whether this watch would be compatible with the 3GS.

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=280378305433&viewitem=&sspagename=STRK%3AMEWAX%3AIT&salenotsupported

Doubt it

I wouldn't buy it. iPhones blue tooth is useless with anything.