Today I jailbroke and unlocked my old iPhone 3G using iClarified and redsn0w. It is now running 4.2.1. However, I went to install Skype and found that it requires at least 4.3. Can I upgrade the iOS to 4.3 somehow? If so, can you point me in the right direction as to how (i.e. a step by step tutorial)?

Thanks!

I forgot to mention that baseband is 06.15.00.

There is a compatibility list showing you what you need to upgrade, try checking that

GUIDE: Which tool to use for jailbreak?

If you have a unlock running, you must do something to preserve your baseband! If you don't you might end up jailbroken but missing the ability to unlock. I don't know about 3G exactly. Still your phone is rather old, trying to unlock it via your carrier directly?

you might try this....

http://everythingapplepro.net/?p=42