Jailbreaking an iPhone means that 3rd party applications can be installed on it (e.g.: apps from other developers then Apple).
Unlocking an iPhone means that all SIM-cards can be used on it. (E.g.: Instead of in the USA AT&T, also the Dutch KPN, the English O2, and all other brands in all countries, as long as you have the SIM-card of that brand
You can.by jailbreaking it or by going to a store that is capable of unlocking phones
No, jailbreaking and unlocking are two separate things.
Unlocking would normally refer to exiting your cellular contract on your iPhone. This should not be confused with jailbreaking, which is illegally downloading unauthorized and often malicious software onto an Apple device.
No. If you are running 3.1.3 (the latest firmware) on any iPhone, then you can jailbreak without unlocking. If you are on a firmware below 3.0, I think you can jailbreak without unlocking. I would like to add that I am pretty sure jailbreaking an iPhone is illegal because of your contract with Apple. Find me on YouTube: TheJailbreakGenius
According to an exemption to the Digital Millennium Copyright Act, jailbreaking and unlocking are perfectly legal right so there is absolutely no need to worry about it. Use trustworthy jailbreak services only.
"Jailbreaking" is hacking your iPhone so it will run any type of app, even those that are not approved by Apple. The process of jailbreaking was illegal until recently, but people have been doing it in order to fully customize their phones, run specific apps or unlock their iPhones so they can choose any GSM Network for service. Edit: First of all most jail breakers don't jailbreak to use any type of app. This is called pirating. As a matter of fact, a lot of jail breakers are against it. Jailbreaking will not allow you to unlock your phone...That must be done by your carrier. This is quoted from a website called jailbreakqa.com "What's the difference between jailbreaking and unlocking? Jailbreaking means removing restrictions in your device's default software so that it can run software not approved by Apple, such as extensions (tweaks) and other packages installable via Cydia. Carrier unlocking is the process that allows an iPhone to be used as a phone on other carriers that aren't supported, such as an AT&T iPhone being used for texting and calling on a T-Mobile plan with a T-Mobile SIM card. Jailbreaking does not automatically carrier unlock your device; they are different processes. See this guide to carrier unlocking options."
By jailbreaking it.
Jailbreaking will void your iPhone's warranty.
Unlocking the iPhone allows you to use any service that requires a sim card.
You cant without jailbreaking it.
Jailbreaking is free.
An iPhone 4 is an iPhone.....