Yes, I have both jailbroken and unlocked iphones (3, 3G and 4). Jailbreaking simply allows you to install non-Apple approved S/W. iPhones will only download software from itunes generally. And Apple must approve all apps that go into iTunes. By jailbreaking, you install an app called Cydia which allows you to install software from other than the iTunes store. Some of that software is free, some costs money and some is pirated.
Unlocking allows you to use an iPhone on a non supported carrier. When iPhone first came out, it was only available on the AT&T network. The iPhone was "locked" to AT&T and if you put in say a T-Mobile SIM card, it would not work on T-Mobile. By unlocking, you could use a non AT&T SIM card and the phone will work on that carrier's network.
Unlocking requires the phone to be jailbroken first. Although, there are SIM card unlock devices that do not require the phone to be jailbroken.
Unlocking is less common because it requires a certain version of firmware, whereas jailbreaking only requires a certain version of the iPhone operating systems (IOS).
I have not looked in to s/w for blocking callers or texters so I am not sure if there are free versions of such software that you could get by jailbreaking the phone.
Also note that updating your IOS version will cause the jailbreak to be undone and will require you to jailbreak again. So if you jailbreak, you have to be sure not to update to the latest IOS version until you are sure there is a jailbreak available for that new IOS version.