Is it my phone or my simcard?

i have gotten a new sim card and i have been trying to like activate it but it isn't working, what i have to do is send a text to a number to a number (and its a free number too) so i can make it so that i get 100 mins and unlimited texts but the text isn't sending and i'm not sure if its my phone or my simcard. My sister says it might be that i've screwed up my phone ariel, my phone is a bit battered up. My phone is a samsung tocco lite and the simcard network is O2.