The very first thing that you need to do is to jailbreak you iPhone. When you have done this, you will have Cydia and Installer icon in your screen.
So, here are the most essential apps that you need to install:
1. Boss Prefs
This app is the combination of all toggle that you can think of including 3G toggle, EDGE toggle, AutoCorrect toggle and much more. So, you don’t have to go to Settings each time you just want to switch of 3G or others.
2. Caller ID Fix 2.1 or 2.2
Depends on your firmware, you need to install Caller ID Fix 2.1 for firmware 2.1 and so on. What this app will do is to correct the phone number so that when somebody calls you, you can see their name on the iPhone.
3. iBlacklist
You can switch off SMS preview here. But in firmware 2.2, you can switch it off in Settings. For 2.1, you need to use this app.
4. ACToggle for Boss Prefs
This is Boss Prefs addon so you can add one more toggle to Boss Prefs that will enable you to turn off AutoCorrect, but in firmware 2.2, you can turn it off in Settings. For firmware 2.1, you need to use this addon.
5. SBSettings
This app enables you to quick open settings toggle by swiping your finger from top left to right. Then you can turn off and on any toggle without leaving your opened app such as Maps.
6. LockDown
I use to lock my phone using Passcode. But each time I slide to unlock, I need to enter my passcode and that is a hassle to me. So, by using LockDown, you can lock certain app that is available on your screen individually.
7. Swirly MMS
Some people say iPhone can’t send and receive MMS.
Less essential:
1. Winterboard
This app will enable you to change the default iPhone theme to wide choice of theme available in Cydia.
NOTE: All this apps are from Cydia, that is only available if you jailbreak your iPhone. This apps are valid for iPhone 2G and iPhone 3G.