Obviously you don't need it, but want it. You will not die a horrible death at the hands of the phone police if you don't get one.
Many people confuse needs and wants and if you invest all your energy in believing that you "need" things, you're on a path to unhappiness in the rest of your life (not to mention the environmental problems that will be caused by always "needing" more).
Admit that you want it rather than need it. Once you do that look at the benefits it will bring, and ask yourself are the benefits worth the near $2,000 (phone for you, your dad, breaking the contract and new phones for your brother and mother). Your dad is already being generous giving you an iMac. If you still want it and think the benefits are worth it, that's fine, but don't pretend that you need it.
As to advice
If you can wait for the 2nd gen, so much the better - you will get a better phone and I don't know what 3g is like in your area, but that would be worth waiting for if it's going to be available to you. The iPhone is a great product as specified, but it will become much better in the future. My guess is the 2nd gen will be out in early 2008 when the iPhone is released in Europe so it can take advantage of the 3g networks here.
If you can break out of the contract without having to pay, that changes the sums pretty drastically. The moving idea suggested above sounds like a good way to try.
Do consider getting a mini rather than an iMac and using the money saved there on the iPhone.
Don't look for charity for a luxury item (and that's what it is). It's demeaning, and offensive when there are people who are actually hungry in this world. Just because someone else did it doesn't make it right. Think about people in your own country who can barely afford to eat, before you even get to poorer countries and the war torn areas of the world.
There's nothing wrong with earning a bit of money. Do some jobs and put the money away. If you've a birthday coming up, ask for money instead of presents and put it away. Don't expect things as of right - you will appreciate it more if you put something towards it (plus if it's your money you will think harder about whether it's actually worth it for you).