To disable iPhone 10MB Download Limit, you need a jailbroken iPhone. The author of VoIPover3G wrote 3G Unrestrictor which solves the problem. Go search for it in Cydia (it costs $1.99). It allows you for example while on 3G/EDGE/GRPS: Make free calls using VoIP software like Skype, iSip, Truphone and other applications Watch TV with SlingPlayer Watch high quality YouTube videos, just like on WiFi Download apps bigger than 10MB from the AppStore Download music, TV shows and podcasts bigger than 10MB from the iTunes Store
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If you lost apps by syncing iPhone to iTunes on a new computer, don’t panic. You could get them back.
You’ll need to authorize the new computer to your iTunes account. Then you can re-download any applications you purchased.
As for connecting to the new computer and syncing, you may get a warning about it, but to my knowledge the settings (mail, calendar, etc) are from the computer to the phone, not the other way around. You may need to create the calendar and email accounts on the computer first, …

This step-by-step tutorial will show you the details about how to jailbreak your iPhone 3GS with OS Firmware 3.1.2 using PwnageTool 3.1.4 for Mac OS X. PwnageTool is a Mac and Mac only tool. There is no equivalent for Windows and no one knows yet when such a tool for Windows will be released.
One thing you need to know is that jailbreaking is different from unlocking. This guide only teaches you how to jailbreak your iPhone. (Read our another post Difference Between Jailbreaking and Unlocking
if you are not …