3G update and data blocking

I have a jailbroken 3G iPhone, on 3.1.3. I did it some time ago and am in two minds what to do now...

I want to install the bookmark app, (which requires ios 4.0 or over), so I decided maybe I should un-jailbreak and update to the latest ios.

1. Do I simply run the update in iTunes and that gets it back to stock? Also what is the view on 4.2.1 on the 3G? Are there still performance issues or is it safe to upgrade?

Ever since I got the iPad I have never used the data on the phone, so I changed my PAYGO account to a daily plan. To make sure the data network is turned off, (and Im not charged for that day), I use that control panel thingy that allows you to turn 3g, wifi, data, etc, on and off without going into settings.

2. I understand that ios 4.2.1 allows you to turn off cellular data from the settings, would this be adequate to completely shut down the data on the phone?, (so I dont get charged).

Is there anything else to consider?

TBH I rarely use the iPhone, it was mainly used for internet and games - which I imagine is the same for a lot of people - now I'm using it as a phone, (rarely), and an mp3 player......and I don't need to pay for both my iPad and iPhone to be on data when there is no need.

I would like to get the process clear before I start anything, so I don't screw anything up, so your help will be appreciated.

Thanks

 

Hmmm, thanks......I'm still in that wary to do anything mode, so I think I'm gonna leave it alone. The drawbacks seem to be outweighing the benefits.

I should really buy a 4s and get over it, but I decided I would wait to see what the 5 brings, (and I'm sticking to it.....probably).

Its a shame, but I can't have everything. Thanks again.