Straighttalk Service, new sim card, iphone 3?

I have straighttalk service, I bought an unlocked iphone 3 but realized my old straighttalk phone did not have a sim card, so I ordered one from the straighttalk website. Now my question is, how do I activate this sim with the unlocked iphone 3? Do I just activate the sim in an old straighttalk phone and then put it into the unlocked iphone 3 or can it be activated from the iphone? I just don't want to put it directly into the iphone without knowing because I only have one sim card and I don't want to ruin it. Also I do not want to lose my phone number that I have had forever. Please Help! Thanks:)

Go to the Straight Talk website to see how to activate your sim card. There is directions on how to switch service from one Straight Talk phone to another Straight Talk phone. If you have more questions about how to activate from a Straight Talk phone to a Straight Talk sim card, you can go to the Straight Talk Facebook page and have someone help you so you do not lose your phone number.

Do not put your sim card into a spare Straight Talk branded phone. If you activate the sim card in a Straight Talk branded phone, it will become linked to that phone and it will be the only phone that you will be able to use the sim card with.