Windows 8 slates will actually have the capability to make and receive phone calls through the cellular network. The first was inconspicuously displayed at a BUILD 2011 session on tiles and notifications. On a slide showing off all the different default layouts of tiles possible in Windows 8 with samples from built-in apps, a "Missed calls" tile lists a number of received calls.
The second, during a video (embedded below) demo by Windows Live, a detailed view of a contact in the "People" app gives the ability to call the person's mobile along with email, SMS and chat. While there's the possibility Windows Live calling is VOIP based, the mobile number would suggest otherwise.
Finally, combing through the system configuration of Samsung's developer preview slate handed over at BUILD, Rafael Rivera found an Option wireless chip for the WiFi, GPS and 3G capability also included telephonic voice capability. The radio supports quad-band 2G and peta-band 3G.
Windows 8 Metro Style Communications Apps:
Using tiles and notifications:
Also, the Windows 8 Slate a NFC chip from NXP. Unfortunately NFC is not enabled in the current build of Windows 8 Developer Preview, but the hardware is ready and was demoed in private (see pic).
Windows 8 will sport APIs that will allow applications to launch URLs, launch applications, share links, initiate peering sessions for applications and games. Developers can also communicate via NFC, but it is not recommended because the bandwidth is extremely limited.
The major benefit of NFC over WiFi Direct or Bluetooth LE connectivity is the fact that the other device can be passive (no power source, a business card) and does not require configuration. One tap is all it takes to make a connection and initiate data transfer.
As the Samsung developer slate is a prototype device, it requires the devices to physically touch which is not a real-world requirement (devices can be up to 8cm apart). Whilst Microsoft will be engaging with OEMs on exact hardware specifications, it inot clear at this stage whether NFC will be a required component of all Windows 8 slates.