We pair a fair bit at Square. We require that all code either be paired on or go through code review, but let each team decide their own process. Some of the teams pair 90+% of the time, and some pair only infrequently.
We're going to change the way people pay. We've got some big backers (http://www.crunchbase.com/company/square), a bunch of really smart people and a product that people absolutely love.
Email me (zach -at- squareup.com), or apply through the site if you're interested.
Does the PCI security standards mention data communication encryption? If so, would this apply to the communication of data from the reader device to the software on the phone?