Is it jailbroken? I have a 3G as well. Upgrading to 4.2.1 I enabled the multitasking switch but it made the phone unusable and unstable. Disabling multitasking

Is it jailbroken? I have a 3G as well. Upgrading to 4.2.1 I enabled the multitasking switch but it made the phone unusable and unstable. Disabling multitasking got the phone back on track (I did lose Airprint). But the phone only occasionally bogs down and never drops a call (I know, hard to believe for an iPhone).