Konami has shared some more info in regards to the link between Metal Gear Solid V: Ground Zeroes and Phantom Pain. It looks like if you buy GZ "early on" you'll get DLC to use in Phantom Pain at launch, which grants you additional resources in your Mother Base to "give you an edge."
This limited offer applies to the first-run retail copies and for a limited time digitally. If you buy Ground Zeroes at any point, you'll get extra "prisoners of war and VIPs," which will be added to the Mother Base staff. Sounds an awful lot like "boost" DLC to me. Yuck.
There will also be a "second screen experience" involving an iDROID App for Ground Zeroes, which functions as Big Boss' in-game communicator and map. It'll available on Android, iOS, and Xbox Smart Glass, and it'll allow you to summon air support, play cassette tapes, or view the in-game map.
Finally, Konami has confirmed that the Xbox One and PS4 versions of Ground Zeroes will get retail discs, and they'll launch for $29.99 (the same as the digital price) -- inline with the 360 and PS3 retail pricing. You'll also be able to grab the game on PS3 and 360 digitally for $19.99.