Is it worth the effort unlock an old iPhone 4?

[Geek-9pm]

Is it worth the effort  unlock an old iPhone 4?
I have an old Apple iPhone four that is in good condition and would like to put it back to work as a cell phone and not be just another gadget to have around. Let me explain.
A few years ago our family started a small business and we all got cell phones from AT&T at that time. Well, to make the story short the business collapsed and eventually we finished up our contract with AT&T. And we ended up with some Apple iPhone fours that we no longer wanted to use.
The idea of unlocking an Apple iPhone was considered to be something that nice people just do not do. It was, some said, against the law to unlock an iPhone unless you're in good standing with the carrier. Well, we weren't exactly in good standing with the carrier because our business had failed and we are not able to pay off all of our debts. You've probably heard that story before.
Well, some years later one of my little smart phones has died on me and I am thinking of now porting over the Sim card into my Apple iPhone four. This is the iPhone four that came before the model 4 S.

On the Internet there are now many posts, some made even within the last year, about how easy it is to not change the carrier for an older iPhone f 4. Well, I'm a little reluctant to try this because the information seems to be either too complicated or even contradictory. So I thought I would just present the idea here and see if there is some users online here that have already done this with the iPhone f4.
Certainly I don't want to have to pay money for anything, I would rather use free tools if available. If I have to pay for anything, I would just as soon go out and buy a new phone. But since I  have the Apple iPhone and it does work .

I already tried putting in a new Sim card and I get some very strange behavior that I do not understand. I'm not sure how the Sim card could've done that. Anyway, I cannot use the phone or install because the screen becomes unusable with the new Sim card. Doesn't make any sense to me, but somehow the new Sim card puts the screen on magnify and I have a hard time doing anything with it. So I'm ready to give up on the project.

But before giving up, I thought I would just ask if anybody here is familiar with the trying to do unlock on the iPhone four. 

[DaveLembke]

I have heard of people "Jail Breaking" them so that they can use them outside of AT&T. I myself avoid Apple products when I can, so I am of no help on this because I haven't jail broken any of these to say how hard or easy it is. Not sure if sharing info on jail breaking is allowed here so I am taking the safer approach of saying the info is out there on how to do it but i am not linking it here. 

[AshtonAsh]

If you got your phone as part of a contract, the first step is to contact your mobile network and obtain a personal unblocking code (PUC). Most networks will provide this service for free after a certain time period, but if you want to unlock before your contract is up – or if you’re on a pay-as-you-go contract – you’ll probably need to shell out up to 20-30$ for the privilege.