If you are a big company , then Ubersmith is the best billing and ticket system for you. I know at least 3 big companies who are using it, 1 of them is a Data Center (Sagonet).
Great support also

__________________
End-user Supported VPS | Hybrid Server | Reseller Hosting
We don't want you to pay extra for features you simply don't need!
Multiple data centers USA | INDIA (with 99.9% Uptime Guarantee SLA )
http://www.odishahosting.com | 1-732-253-0169 ( sales)