I am 99.9% sure it is through the cloud and not bluetooth or the coil, the coil simply initiates the 'handshake'
From the website:
The next generation of Touchstone technology makes HP devices work better together. Easily share a website with your Pre3 simply by touching them together.5,6 Receive text messages and answer phone calls on your TouchPad so you don’t miss a thing.2,3,4 Start reading a website or blog on your tablet and then touch your smartphone to take it to go.5,6 We’re building more connected devices so you can have a more connected experience.
5. Requires HP TouchPad with webOS 3.0 and Pre3 or Veer with webOS 2.2 or higher, both products having the same HP webOS account. Viewing URL web page content requires data connection via Wi-Fi or cellular connection.
6. Within wireless coverage area only. Actual speeds may vary. Email, mobile number, and related information required for setup and activation. Required data services sold separately; unlimited plan recommended and may be required. Not all web content may be available.