How do u switch sim cards?

i screwed up my new sim card and now im just gonna use my old one but wen i put it in.. it doesnt work do icall the company and will they be able to verify the sim card change over the phone???How do u switch sim cards?
Yes, the company will need to activate it. Sometimes they do go bad, but try getting it activated first. If you need a new SIM card, I'd try ebay. I got one for less than $10 and my carrier wanted about $40.How do u switch sim cards?
it doesn't work cause when you got your new sim card they cancel the other sim card. i suggest going to your cell phone store (at%26amp;t, t-mobile, etc) and tell them that you messed up your sim card and that you need a new one. they would usually give it to you for free if you renew your contract. and that's if your eligible for an upgrade.