Ever since November last year, when Google first unveiled its Android plans, and following a live demo of the platform less than a month ago, questions about the promised deadline have started to emerge.

Some developers have complained that Google’s constant change of the software makes it hard for them to create Android-compatible applications.

The Wall Street Journal reported that handsets are likely to hit the market not earlier than the fourth quarter of this year, possibly at the beginning of next year, due to the inability of some partners to meet the promised deadline.

Among the names given by WSJ were Sprint Nextel and China Mobile, whose chances for a 2008 launch are reportedly close to zero.

Sprint Nextel is reportedly not able to deliver an Android-based phone this year due to some management changes that might turn its attention to another matter: a 4G network.

China-Mobile reportedly admitted its inability to deliver the phones by the end of the year, and according to sources familiar with the matter, they won’t do it earlier than 2009.

On the other hand, T-Mobile seems to have remained the only one to keep its promise and deliver the Android headset by the end of 2008.

This is not the first time rumors on Android delay have appeared, but Google hasn’t confirmed any of them.

In an e-mail sent to BetaNews, Google said they remain on schedule for the second half of the year launch, while at the same time saying they are excited to see the momentum built around Android by carriers, handset manufacturers, developers and consumers.

Earlier this month, Google also stated that it is on track with the open-source mobile OS and that its partners are also ready to ship Android phones before the end of the year.

The question is: who to believe? Google will find it hard to meet the deadline due to its complexity and the necessity to meet the requirements of so many types of hardware platforms.

On the other hand, Andy Rubin, director of Mobile Platforms at Google, was as optimistic as it gets during the I/O conference last month, saying that Android-phones will definitely come out in the second half of this year.