Sharing contacts in iOS 6 is pretty much the same as that in iOS 5. Apple has, thankfully, not made any changes to this particularly important feature (unlike Groups to which Apple has made a lot of unnecessary changes).
People often need to send contact details to their other friends on iPhone. They can do this in two ways: send email or send iMessage. Both will use your data but in the even that iMessage isn't working, the contact detail will be sent across as MMS. In that case, your text(MMS) allocation will be used.
To share a contact from your iPhone to another iPhone in iOS 6.x:
Step 1: From the Contacts, choose the contact you want to share
Step 2: Tap on ‘Share Contact'
Step 3: Now, if you have iMessage enabled, you should see two options:
Step 4: Tap on ‘Message' to send the Contact detail as an iMessage
Step 5:Tap on ‘Email' if you want to send the contact as a .vcf file
When the message is sent as an iMessage, the other person would receive it on his/her iPhone and can add to his contacts by simply tapping on the iMessage and following the options.
When sent as an email attachment, your friend would have to open the attachment after which he can select “Add to Existing Contact” or “New Contact” as is the need.
If you have iMessage disabled, tapping on the Share Contact will directly add the contact details as a .vcf file to the email and the Mail app will open.