What’s better than a deal that turns your current customer base of 150,000 small and medium-sized businesses into a potential field of five million?

The same deal, with an undisclosed but “multi-million” dollar investment thrown in for good measure.

That’s how the year is beginning for Tradeshift. The company announced that it has formed a partnership with Intuit, integrating its e-invoicing and business transactions platform with QuickBooks. The new free app, which connects to customer’s Tradeshift or Quickbooks accounts, will be available first to QuickBooks users in the United Kingdom.

The company also announced a significant investment from Intuit, which will join Tradeshift’s board of directors. Although the amount was undisclosed, it has been characterized as “multi-million”.

Newly available to QuickBooks users, the app will also be an opportunity to further test Tradeshift’s social networking approach to business. CEO and founder Christian Lang has said that “invoicing is one of the few business processes that’s really viral.” Thanks to Intuit, he’ll now have five million opportunities (and undisclosed millions in new capital) to help prove his point.

See Tradeshift in action in this video from their demo at FinovateEurope 2012.