You can take it to what ever company that sim card belongs to and I am sure they have some way to read it and see what the number is.
You can also stick it in a phone, and they should some where display the number, I am assuming your have an iPhone since you are in the Iphone section, the iphone displays the phone's number at the very top of the contacts list, your have to scroll up a bit to see it. (you need to access the contacts from the phone app, in the contacts section or it wont show the phone's number)