OLO, a web and mobile online ordering service for restaurants, is celebrating a lot of things: bigger office space in New York’s South St. Seaport district, hitting the 1 million customer milestone, adding new restaurant partners, and plans to launch its long-awaited GrubHub integration, nearly a year in the making.

For those unfamiliar, OLO is a B2B(toC!) service that allows customers to order ahead and pay online or on mobile (where available) for takeout and delivery at local restaurants. Customers input their order which is then sent directly to the business’s POS system, with OLO snagging a percentage of the transaction fee along the way.

OLO currently powers the online ordering systems for several big-name chains, including Subway (its NYC locations), Five Guys Burgers & Fries, Cold Stone Creamery and SONIC, for example.

It has also just signed an ice cream chain (hint: makers of the delicious ice cream cakes), a U.S. barbecue chain, San Francisco bakery La Boulange, Fatburger, and the South African-based Nando’s, which operates stores in the Washington D.C. area. This year, OLO will begin to power the overseas Nando’s locations, including those in the U.K. and Australia, too. The company also plans to expand into Latin America and Canada in 2012.

In March of last year, OLO announced a partnership with online ordering provider GrubHub, which, until then, had been focused only on independent restaurants, not chains. The partnership makes OLO the exclusive provider of restaurant chain ordering to GrubHub. Going forward, OLO will provide both restaurant and menuing information to GrubHub for its partner restaurants, allowing GrubHub customers to place orders and make payments via GrubHub for the OLO-powered chains.

Those integrations are now just a couple of weeks away from launching, starting with OLO-powered restaurants in the NY and Chicago areas. By the end of March, all of OLO’s restaurants will be live on GrubHub.

In addition to powering the ordering systems of major chains, OLO also runs GoMobo, a B2C service that lets customers order online or via text. But the company shifted its focus from B2C in December 2010, when it acquired the OLO.com domain name. “The name change was symbolic of the shift from being a B2C company…to being the backend technology for big brands,” says CEO Noah Glass.

For restaurants, signing up for OLO brings hundreds of new customers. “For every new door that we open, a restaurant will get 250 new customers joining the service,” Glass says. When brands launch on mobile (OLO provides white label apps, too),  they see even more signups – around 400 to 500 new customers, Glass estimates.

Although OLO is doing well now, it’s early days for the up-and-coming company which saw 10x growth over the past 16 months, and now counts over 150 restaurant brands and thousands of individual restaurant stores as partners. “There are 600,000 restaurants in the U.S. that we think would work well for the service – it feels like there are many more brands for us to sign,” Glass says of the company’s plans for growth.

“More and more customers are looking for self-service experiences – not just in food, but in banks, airlines, and online shopping – we’re taking one of the lowest tech industries and bringing that self-service capability to the restaurant experience.”

OLO received $7 million in additional funding from RRE, Founder Collective, and Core Capital in 2008, bringing its total funding to date to $8.75 million. Glass says they’re not looking to raise additional capital now.