British Telecom this week released an update to its Web21C software development kit that adds new unified communications capabilities, a move BT execs said would let any developer build a Web/telco mashup to compete with services like Google’s Grand Central.

The new CallFlow capabilities added to the SDK focus on interactive voice response, enabling third-party developers to use the BT network and APIs to integrate voice capabilities into their Web services, said JP Rangaswami, managing director of service design at BT. Additional CallFlow call management capabilities will be added to the SDK in the coming weeks, he said.

The new IVR features join existing capabilities exposed via the SDK, including messaging, conference calls, voice calls, authentication and inbound SMS.

Web services like Google’s Grand Central let users route calls to special numbers and manage their calls and messages via a Web interface. Grand Central recently came out of beta, though the service has not been pushed hard by Google and has not been integrated into its other online apps.

Though BT’s big-picture plans include exposing a wide array of capabilities via APIs and SDKs – including virtualized storage/data center capabilities, BSS/OSS capabilities and carefully-vetted access to customers and customer data – the initial SDK release is focused on the network.

“The first version of the SDK was about giving someone the ability to build a softphone you could embed within other apps,” Rangaswami said. “With CallFlow, we’re doing the same thing with IVR. Rather than give users a Grand Central-style application, we’re giving developers the tools to build their own.”

Since its July 2007 release, BT’s Web21c SDK has been downloaded 8000 times, with 300 production applications and 4500 sandboxed trial apps created, according to BT.

In a wide-ranging Telephony interview, Rangaswami reiterated BT’s master plan with Web21C: to create a platform to enable a wide variety of next-generation communications businesses, sometimes with BT at the center, sometimes not.

“When we say that BT is becoming a platform-based company, you have to understand what that platform means,” Rangaswami said. “For us, a platform means a multi-sided marketplace. Our business model is that this platform enables a variety of business engagements, open and multi-sided, and that many transactions take place on this platform that don’t get into the hands of BT as a network operator.”

The Web21c SDK continues to roll out with regular ninety-day updates, Rangaswami said.

Though the Web21c project has many tentacles, Rangaswami said BT aims to have the core SDK capabilities released by the middle of this year, with a goal of completing the core engineering for the whole platform by March 2009.