You're not going to like this answer, but I and everyone else on SO will tell you that developing for a jailbroken device is 10 times worse than developing legitimately with a developer account. It's not really that expensive, and if you don't have a mac, a low end Mac Mini isn't all that costly either. If you would just want to get some mobile handset practice in, might I suggest developing with Google's Android. The SDK is free and you can get a nifty plugin for Eclipse that has a device emulator as well as a GUI builder. The only downside is that the device support is minimal at the moment. But hey, you can be on the bleeding edge of a technological revolution.