[gr8fl4porsche]

4.2.1 is not jailbreakable for the masses right now. You can jailbreak it by installing a custom firmware but it will be tethered meaning that if your battery dies, you cannot boot your phone without plugging into a PC/Mac. If you had to reboot for any reason, the tethered jailbreak would need the computer to allow the phone to turn on. Not really a viable option for most folks.

Don't confuse a tethered jailbreak with tethering internet - different uses of the same term.

There is rumor of a 1-click non-tethered jailbreak (Green Poison 2) coming out soon but it is always a waiting game.

Bottom line is never update an iPhone's firmware unless you find the new version offers something worthwhile. Most updates offer no real benefit to the end user.

I will let you know when the new JB comes out so you can get your tethering installed. The MyWi app costs $20 but works perfectly. Creates a wifi hotspot as well as a USB option. Much better to pay a one time fee rather than per month.

If you went the ATT route right now, you would have to give up your unlimited data plan, sign up for a metered plan and then pay an additional $20 per month for the privilege of using the exact same amount of data. Essentially, ATT charges you double for less data usage. Who would buy into such a horrible plan?