It's a webservice I hacked together that sends iMessages from my old MacBook Pro. :-)
It was my understanding that German mobile numbers are written locally starting with 01? [1]
e.g. in Australia, my mobile number would be 040x-xxx-xxx. The international version is +61 40x-xxx-xxx. When you select Australia, it will show 04.
(OK, I now see how this could be confusing; my apologies.)
[1] http://en.wikipedia.org/wiki/Telephone_numbers_in_Germany#No...