[UPDATE] Patapon 2 will not be available on UMD
According to an inside source speaking with ArsTechnica, Sony plans on releasing Patapon 2 as a download-only title with purchase vouchers being sold at retail locations. This source -- which has been a solid foundation of inside info in the past -- also notes that Patapon should retail for $15 on the PlayStation Store while its physical counterpart will ring in at $20 a pop. While it's odd to see two different prices for the same means of operation, it does give way to the next PlayStation Portable, which may discard UMD entirely.
Furthermore, the source also indicates that these vouchers will also be purchasable through other online retailers as well. The problem with downloadable titles on the PlayStation Network is that you can always share them with up to four other people if you'd like. Hopefully Sony has some sort of plan in order to prevent gamesharing in this specific case, or the company will be looking at a major loss of revenue on one of its more unique titles.
UPDATE: This rumor has been confirmed by Patrick Seybold, Senior Director of Corporate Communications at SCEA.
"We're considering a digital only format for the Patapon 2 release as a one time test case as we continue to explore consumer preferences for digital content," reads Seybold's statement. "The downloadable game will be available on May 5th at both retail and via the PlayStation Store. We remain focused on providing superior games and entertainment experiences in both the UMD and digital formats and are working closely with our partners to deliver the best PSP line up in our history."