I've just bought a couple of the E3 emailers at Toys R Us. They have them on sale at £29.95 each. I hope to be doing a little bit of hacking on them in the near future...
I've just bought mine from Argos - they're ~£30 there too. Interestingly the Amstrad site says they're "around £29" but not many places seem to have them for that price yet.
I'm a bit disappointed though that it doesn't even work as a plain old phone until you register! I thought at the very least I'd have a working phone if I couldn't do anything else with it!
I'm going to attempt Jonathan's method of using Asterisk to get the E3 to call a machine with a modem on it and see if I can get the phone to think it's registeed, but I think that might be a tall order. I'll let the list know how it goes, and no doubt be back for advice!!
Cheers James