My iphone 2g 8gb is lock can only use emergency call?

Verify the sim card in another phone, probably you have a damaged sim card .

Yes. Unless your iPhone is locked by the carrier in which case you have to use it with that carrier's plan.

All open (unlocked) phones can be used with pre-paid and post-paid SIM cards.

To check if your iPhone is locked, put ANY working SIM card (correct size) into your phone. If it does not recognise the card, then you most probably have a locked phone.

Hope this helps

Are you using an AT&T Sim Card?
IF you are not then the iPhone has to be unlocked in order to use with a non AT&T sim card.

You can google how to unlock iPhone or post a reply with the Model of the iPhone (2G, 3G, 3GS or 4) and the firmware Version you currently have.

To view the firmware version go to Setting-->General-->About--> Version

Please make sure you've SIM card inserted in the phone and then connect your phone to itunes.

It seems that your iPhone 2G is in need of activation. To accomplish this, there are 2 ways:
A. (With AT&T as your service provider)
1. If you do not already have an AT&T sim card, contact AT&T and ask for an AT&T sim card to activate service with them. Choose your plan and insert the sim card in the iPhone.
2. Connect the iPhone to iTunes and you will be prompted to follow a few steps to proceed with the activation process.
3. Sync your iPhone for the first time.
Once completed, you will have your iPhone activated and ready to use on the AT&T network.

B. (Without AT&T as your service provider)
1. You will need to download an application to jailbreak your iPhone. (This will essentially remove certain restrictions on your iPhone 2G that prevent you from utilizing your iPhone on another network, among other things).
2. Connect your iPhone to the computer and run your jailbreak application of choice.
Once completed, your iPhone 2G will be activated and jailbroken. The "emergency call" message will disappear, though you will be prompted with a "no sim card found" message until a sim card from AT&T (or another GSM carrier) is placed in the sim tray.

Find somebody with an AT&T sim card, put it into the phone and plug it into itunes to get it up an running. Otherwise if your not using AT&T you're gonna have to jailbreak the phone to use it. If your a prepaid AT&T customer, you can activate it but you gotta call AT&T at 800 331 0500

yes

Check if it's in the right way and plug it into the computer.

It depends on what type of plan you want such as a Prepaid or Post-paid plan. Post paid plan is where you have so many minutes per month and you have data plans available as well. You might be able to go in to AT&T and ask how much pre-paid plans are and if they have internet useage on them you will be able to take that sim card out and put it in your iPhone. Other wise if there is no AT&T carrier in your area, you can unlock/jailbreak your iPhone and then you would be able to use it with any carrier that takes sim cards. I personally use QuickPwn, but if you are going to do this just make sure that you are NOT running 2.2.1 on the 3G as you will not be able to unlock the phone, and you will have to get a turbo sim in order for it to be unlocked. Hope this helps you out!