I always thought a wristwatch cellphone was just a Dick Tracy cartoon idea, or a prototype that would never make it to market, but apparently a company in Australia is actually going to be releasing a bluetooth enabled triband gsm watch phone very soon, with more models to come. Check this site out:
http://www.mymobilewatch.com
It's cute, but a bit on the expensive side. Still, it's an incredible feat of engineering to make a workable phone this small. Hope they do well.
Wrist watch phones that make it to market are a rare event. There was a Japanese Wristomo watch that worked on their proprietary handyphone system. There also was a bulky watchphone made a while back in China. Also some bluetooth enabled watches have been made, but that's different from making an actual watchphone.
Phones/Wireless Devices: Doogee S90, Isatphone Pro, Amazon Kindle 3G, SkyRoam MiFi device, Karma MiFi device, AT&T Liberate MiFi device
Sim Cards: T-Mobile (Mint), AT&T (Mifi device or Kindle), Koko
Satphone: InMarSat
Broadband US Wireless Data: AT&T postpaid, Sprint (Karma Mobility prepaid)
Broadband International Data: SkyRoam
VOIP: Skype