Although Apple is against jailbreaking the iPhone, iPhone users do it anyway regardless of what Apple want, and this is mainly due to Apple limiting some functionality due to security reasons and the like, but we have a couple of iPhone applications for your consideration that make it possible to do more on a 3G connection with your jailbroken iPhone.
Both iPhone applications have been suggested by Bob Bhatnagar over at iPhonefaq; the first of which is called Auto3G and what the app basically does is auto-switch your iPhone 3G connection over to EDGE every time you lock your iPhone as this can save battery life.
Version 2.0.3 of Auto3G also auto-switched the device back to 3G as soon as the user wakes the iPhone from sleep, and is available for $5.99 from BigBoss.
The second suggested application is called My3G which basically tricks the iPhone into believing it is on WiFi when actually it is on a 3G connection and the user can also view YouTube videos and enter VoIP calls without a real WiFi connection, and much more.
The user can also select which applications are My3G enabled and it features an indicator to let you know when the iPhone is switching from 3G to WiFi. My3G costs $3.99 and is available to download from the Cydia App Store.