David, en4,
I use an ex-Ericsson T610 datacable to talk to the E2. It's USB-powered and contains a PL2303 USB-serial 'uart' and has no line drivers.
Ericssons have 3.3V interfaces whilst the E2 talks at 5V - I cracked mine open and rewired the 'VccIO' pin (my own name - I can't remember the real name, it's the I/O pads power supply which may be greater or less than the 3.3V logic supply to the PL2303) to 5V instead of 3.3V. In fact my particular cable has a switch on the side (charging on/off it seems) so I can switch 5V/3.3V operation (for other projects).
It's very nice, I'd highly recommend going down this route rather than making all sorts of separate boards and, as has been mentioned, trying to find a +5V supply for them.
(Actually if you CBA to crack it open and change it from 3.3 to 5V it should work at 3.3 too. (though of course the inputs may not be 5V tolerant on your cable - consult the data sheet, a good proportion of the el cheapo no-brandname cables have the PL2303 in though.))
Best of luck,
Matt
PS: I believe Nokia F-Bus also runs at 3.3V