provided by Star2Billing S.L.

I seem to remember another thread asking exactly the same question. The reply is still: that's how it ships!

as I remember, there's nothing you need to do.. just use your email to login as normal. no changes needed. correct me if i'm wrong.

I didn't have to patch anything. It's working with email out of the box

Glad to hear it. There's a lot of rough edges been knocked off it over the last 6 months, and I think it's reasonably shiny at the moment.
As v1.3 is now in maintenance there'll be no new features, only bugfixes and small refinements. It's already proving to be quite stable for a number of customers of mine, and things should only get better in that regard for future v1.3.x releases.
There's already quite a lot of new stuff to look forward to in v1.4 (trunk) too, so the future of A2Billing v1.x looks good.
That said, there's a few of areas in which A2Billing could do with being overhauled as they limit maintainability or flexibility. To this end Xrg has made an excellent start on v2.00. This is a very long term project (you won't see anything usable for quite a while), but his new framework already shows much promise. V2.00 is almost completely incompatible with v1.x, but I'm sure at least rudimentary migration scripts will be available by the time most users will want to run it.