My iPhone won't work as a phone?

I found my iPhone in the city, I took out the sim card, but when I put in my own sim card it won't work.
Whoever owned it before me must have locked it from the phone service company. Please Help I'm DESPERATE FOR A GOOD PHONE AND NOT A NOKIA

Well if you said no to a Nokia your screwed a Nokia Always works.drop it in a pool pick it up and change the battery boom good as new.