[otrs] Billing software

Howś the list doing Been lurking for a while but finaly broke cover to ask a question. I have been using OTRS for about 6-7 months purley as a trouble ticketing solution + it helps me keep trak of customer info. Now the boss want to try and use it for billing as well. Problem is he has not decided on which billing/accountancy software to use or whether we will outsource it. Does anyone have any tried and tested suggestions? (there was note of someone using ooo to generate invoices, not sure he would go for that as he is using a similar Excel soultion at the moment :( regards richard