R all sim cards the same size? because I took my sim card out of a Samsung sgh-a237 and it seems to wide to fit in my nokia!

go to your local phone shop and get your old sim card cut it will cost you about £2

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To Unlock samsung SGH 237 from Sim lock or network lock use the unlock code...You can get the unlock code from Classicunlocking and unlock it easily...

Make sure you have inserted the sim card the right way.
If you have inserted it correctly, make sure the matel plate is firmly fixed, you should feel a slight pop as you fix the metal plate

do you mean puk code?Puk code can be found in the card where the sim card attached when you bought it..and can not be found in any celphone

Hi, DONT CUT SIM!
Sim cards on the samsungs slot into sim reader which is found under battery. If you remove the battery you should see where it goes. The slot you are referring to sounds like the memory card slot which is an expansion slot if you want to increase the memory size for file storage. Hope that helps?

WOW! what a process! I don't know how you kept track of all that but , good job! Try this. It's a maybe, but better than nothing,

TEMPORARY UNLOCK:
Put a non-accepted SIM Card and turn it on. Type *#9998*3323#. Press Exit. You will get a new menu. Select Malloc Fail.

In newer phones:
#*7337#

At this stage, call AT&T is probably the best bet. Call back until you get a more knowledgable technical support rep.

Any SIM card that is activated (not expired or cancelled) by the issuing carrier should work, assuming that your Samsung phone operates on the correct frequencies for the country you are in.

You need three things to be true for all this to work.

1. Your phone must be unlocked. (You have this one OK)
2. Phone must work on the frequencies for your country (I don't think your Samsung covers European frequencies, from the web sites I checked)
3. You must have a valid SIM card, either prepaid or on a billing contract

Having said that, the price charged for your calls will vary widely from carrier to carrier. For occasional use, the cheapest thing to do is to buy a prepaid SIM that is issued in the country you are in. I would NEVER take a US SIM card to Europe and use it there unless (a) price was no object; or (b) I absolutely HAD to be reachable by others using my US phone number.