Every singer as an A4 folder of songs they bring to rehearsal, but now they can have all of their lyrics with them all the time, on their iPhone. You can also create setlists of songs which can be edited and reordered. Setlists and individual songs shared with the rest of the band by email, iMessage, Airdrop, or print them out.
Rather than searching online for other other people's versions of songs, this app displays your lyrics, which you've formatted as you want them on your computer. You can create them in Pages 09, Doc, pdf, rtf or txt format [Unfortunately Apple don't yet allow apps to use the new Pages 5 format - this should be resolved in a future iOS update] then simply transfer them to your phone using the iTunes file transfer system (on the Apps tab for your device). While primarily designed for singers, the new improved pdf handling makes PDF scores look amazing, so the whole band can get in on the act.