For UMPCs in general the platform is wide open. Many OEMs are choosing to install Wifi/BT as standard and include a PCI-Express MINI slot on the mobo which enables the OEM to drop in the required 3G/WiMax moduile as required. FOr example, .the Samsung Q1 Ultra ships with or without a 3G module installed.

For Centrino Atom MIDs (definition: Silverthorn/Pulsbo based sub 5" devices running Moblin-compliant OS) the story is slightly different. I don't have the authoratative answer but I understand that all will come with Wifi/BT and will offer a Micro Mini PCI-Express slot (half size I believe) Intel will either provide their own Wimax card or Option will provide the 3G card.

As for voice, its not clear. The questions would be, do Option provide a voice-capable card, does Moblin provide the hooks and is there a UI for voice operations. You would also have to consider audio hardware on the platform. (e.g.  is the device designed as a speakerphone with noise canceling mics or does it require a headset - BT or cabled)

As for a list of devices, UMPCPortal, the site I run, contains the most complete database of devices with over 140 models listed. You won't find latests prices, only guidelines prices as this changes daily and varies between territories. Here's the link to the product database. Hope it's useful.

Regards
Steve 'Chippy' Paine.