btw, if you want to spend some money in it, then you can get factory unlocked iphone from apple too to make it work with any sim in the world, but this will be only unlocked one, not jailbroken.

to reverse the unlock/jailbreak, simply update your iPhone with the latest version of the firmware with iTunes, and this will replace the jailbroken OS with original one

Other than that, most people who jailbreak, also know how to unjailbreak (if they really know what they are doing), so you can use their services for the same purpose.

thanks- good to know. But when I return to the US can I reverse the unlock/jailbreak so that I can update with itunes and get new apps, etc?
Also do you know a professional in karachi who can set up the phone?

yes it will work. But only if you follow the process correctly and don’t update it with itunes. If you are not comfortable with the process then get the services of some professional or some one who have done it before.

I am personally using an unlocked and jailbroken iPhone 3G with all apps and features (and yes, on warid sim)