Normally, USPS.

In fact, more than 50% of credit card production costs are postage.
http://www.creditcards.com/credit-ca...ocket-1276.php

With ever increasing cost of stamps and uncertainty of the USPS, most banks are looking into moving towards instant issuance of credit cards at local branches instead.

http://www.bellid.com/solutions/emv-instant-issuance
http://www.datacard.com/financial/in...ndustry-topics

In the future, getting a credit card would become more convenient by just walking into a bank branch and getting the card printed and personalized right then and there instead of waiting for the mail-person to come and deliver it to you.