Want to find out how to easily share someone's contact information on your iPhone? Simply go into your address book on your iPhone, tap on the contact you'd like to share and you'll see an option at the bottom to share the contact. When you tap that, you'll be presented with an option to either MMS or e-mail the person's information. Choose your option and the respective app will launch by itself.
If you're sending via MMS, you have to choose who you're sending it to and click send.
Sending by e-mail isn't much different, just type in the person's email address you'd like to send the contact card to (or choose them from your address book) and you're contact will be sent on it's way!