I have an Electric Imp and love the way I can move it to a new network and connect it, using the iPhone or Android app.
I am not in the position of doing the same with an ESP - I can't program an iOS or Android app, for a start - but I wondered whether using some other sort of interface would work?
A keypad, a touch.screen, a built-in web page with a predefined SSID, so you could connect using a mobile device using the predefined SSID, access the device and add your foreign network details?
What methods have been tried?