Currently, I am not planning on purchasing a dedicated device to serve as an intermediate between my ultraportable and a phone although that is the ultimate goal. Once I can establish that the network works and works well enough, I'll probably move to something with good battery life and portability. the UMID M1 doesn't look too bad as long as you have spare batteries. The n810 WiMAX edition is an abvious alternative. UMPC Portal ought to have a wide range of choices and is an excellent source of information if you are in the netbook/MID/UMPC market.
Edit: Chippy from UMPC Portal recommended the Viliv S5 as a device that may come close to meeting the heavy battery life requirements. I also remembered the Raon Everun and have asked him about its potential to provide a full day's worth of charge especially with an extended battery.