Default [Q] Only developer unlock Nokia Lumia 710

Hi, I am developing an app for windows phone and I would like to use my parents phone for testing (Nokia Lumia 710). I don't need any fancy stuff like custom roms since the phone isn't my and I dont want to lose data from it... I need just developer unlock. Is it possible to get it for free and without losing data?
Windows Phone on Android? Dual boot?