Switching iPhones?

[HUNTER1]

I'm getting ready to replace my 4s with Iphone5. My 4s is jailbroken on 4.2.1 and never updated with latest firmware because I always had problem restoring it. I will get the 4s unlock by AT&T once deactivated. My question, will it function just as well on 4.2.1 jailbroken if I never restore to latest firmware? thanks

 

[Skull One]

Just for clarification. The iPhone 4S never had an iOS lower than 5 preinstalled on it. So the OP has to be referring to an iPhone 4.

 

[HUNTER1]

I'm sorry. It's 4s 5.0.1