Does jailbreaking an iPhone 4 un-network lock it also?

I just traded with a mate for his iPhone but it's network locked to Telstra. If I jailbreak it will it unlock it so I can use my provider? Also if I jailbreak it can I still use the app store as I have a few apps I need, thanks.

Added (1). My mate bought it 2nd hand off ebay, doesn't have contact with the seller either.

Added (2). Also ios is 6.0.1

Forget jailbreaking for a bit and call your mates service provider and ask them to unlock it for you at no extra charge since the phone is no longer in service:-)

No, Jailbreaking will not unlock it But Yes you can unlock it after Jailbreaking. Below are the steps to Jailbreak and unlock

If your iPhone 4 is on iOS 5.0.1 or higher, Just download the latest version of RedSn0w software and follow steps given in this guide

http://www.redmondpie.com/jailbreak-ios-5.1.1-untethered-using-redsn0w-0.9.12b1/

After Jailbreaking

Go to Cydia > Search for 'UltraSn0w' and Install it. After installing Reboot and your iPhone 4 will be unlocked.