Google has explained the choices it offers developers, in a public demonstration of the Android software development kit, in London.

Android will be different from the leading smartphone operating system, Symbian, because it is open source, said Dave Burke, an engineering manager within Google's mobile team, who also defended the search giant's decision to use its own flavour of Java and not to support the popular C++ programming language, to an audience of mobile developers at the Future of Mobile event in London.

"Software is an increasing percentage of the cost of handsets, and Google feels that there is not enough innovation," he said, adding that an open source environment will provide a really great phone experience and reduce the cost of a phone by ten percent. Android will provide a unified platform that nevertheless allows delivery on multiple devices, he said.

By comparison, operators pay a licence fee for Symbian, and it is fragmented between the S60 and UIQ platforms, he said.

The big difference between other Linux phone platforms such as LiMo and OpenMoco, said Burke is: "This is real. It has a big momentum with key partners."

Burke developed a small program, with help from a clearly favourable audience, and then faced probing questions on the details of the environment.

Games developers in the audience asked why there was no C++ support, saying this would allow faster response times and better control, but Burke denied it: "We have our own APIs," he said. "We have a better flavour of Java."

Asked about Android's security model, Burke said "We are trying to do a more simple permission system," he said, explaining that Android takes the Java Mobile Information Device Profile (MIDP)'s security model, and uses it to produce something "sensible" so the environment is secure but "the user won't be bugged by questions."

Although Android will be open source, the source itself won't be released until late in 2008, when the first Android phones go on sale. "There's a lot of intellectual property in this," explained Burke, so the providers of the technology have decided not to leak it until the environment is established. "This is version 1.0. There will be bugs in it. We don't want to support and open it until it is ready.

Android will be open, but device makers will be free to limit and reduce it, Burke confirmed: "That is always a problem," he said, adding that Google would push the good user experience, and hoping that "the common core will be so good that device manufacturers will just take it." Others in the audience queried Google's overall open source strategy, in choosing the Apache licence and not GPL.

Burke is editor of VoiceXML and related W3C and IETF standards and was previously the chief technical officer and cofounder of Voxpilot.