depends on what you want/mean. if you can get your phones guts to fit inside the gophone case then itll work, but if you want it to work as a gophone at the same time as a cellphone its probably unlikely.
If your sis wants the cellphone to be like the gophone, what she can do is buy the gophone, ask some techie guy to work on the gophone so that it can function as a normal cellphone and at the same time she can become a Go-onger as well, presumably Go-onYellow ^^
Doing this seems a bit... unpractical. Seriously, are you in that dire need to get your cellphone to become a go phone?
Theoretically, it SHOULD work, but it will be a pain in the ass to do, getting the buttons to align correctly and whatnot. Then you gotta make sure you get signal and you can use the microphone properly, let alone look at the screen. :disappoin