Are there any good billing/help desk in one hosting software?

Dram Plus in www.dramsystem.com

Modernbill has a very basic support system in it. Your best bet is to probably get seperate systems and make some code to intregrate them. :)

Adam

http://www.clientexec.com/newsite/product.php

Has an invoice manager and a support center.

Good luck in your search!

You might want to check out "ubersmith"

Gives you both options. Doubles up as a support desk and as a billing manager.