The US  Postal Service is  testing Mobile Point-of-Sale (mPOS) Technology:-

The Postal Service is going mobile.  They tested a new point-of-sale technology over the busy holiday season and they say they processed more than a 100,000 transactions. Postal workers can scan and accept prepaid packages or sell stamps and other products before customers ever make it to the counter.   The goal is to cut down on the time customers spend waiting in line for most routine transactions. The new technology   is called Mobile Point of Sale (mPOS), and uses a modified iPod Touch and portable printer to "scan and accept prepaid packages, scan package pickups as delivered, or sell stamps, ReadyPost and other retail products." It'll also spit out Priority Mail flat-rate postage.