You should still be using something like TestFlight. Emailing builds arounds is nice but reaches critical levels of headache after the 5th or so beta.
There's instructions on how to do this at: http://nachbaur.com/blog/building-ios-apps-for-over-the-air-...
Although it saves you from having to email large files, you do still need to collect your users' UDIDs and add them to your provisioning profile (embedded in the app).