Is there a way that I can hack a tamagochy and make my own monster?

I wanted to make a pokemon tamagochy hack, since it seems like something not so hard to do. I know it probably wouldnt take too much time for a programer to do the program itself, but im completelly clueless about this stuff. but doesnt that seem like a cool idea for a present to my little brother? :D i was gonna gut the tamagochy and make a pokeball shapped case for it, and make it so the little charmander eventually evolves to charmillion then charizard. and since the new tamagochys hagve that wireless communication, maybe one could get crazy and make a little battling system kinda think. that just seems to awesome to happen sometime soon, but i was wondering if someone had a way to get it done. dfosafjdsijfds w00t w00t!

You'd pretty much have to build the whole thing from scratch. Software-wise, you're starting from nothing. You could probably figure out how to connect the LCD to an arduino, which would give you a huge step forward in hardware but also make the project much bigger and costlier. In all, I'd say it's not worth the endeavor. The cost for developing this would be comparable to buying a gameboy advance and a few Pokemon titles, much more if you were to add wireless capabilities.
My guess is that you wouldn't be able to do it without replacing most of the circuitry. Toys like the tamagotchi would be hard coded, in some form of ROM, most likely a small mask rom built into the processor die.