My friend had his 3g hacked and the reason he doesn't hack his 4s is cause it'll be unstable. My other friends with 4s who have had the other four iPhones before are afraid to hack also because of this. And when they do they experience issues.
An iPhone is an app machine. Its a phone designed so you can download a million apps. That's why they have that whole grid system etc. The iPhone was designed around applications.