Developers have been working on a branch of code called "Cupcake" for the Android mobile operating system from Google. The update for Android promises major improvements to the mobile operating system. G1 users are anxiously awaiting the update, but T-Mobile is saying "no" for the moment.There's a reason why users of the HTC G1 are craving cupcake. New screen shots seen this week show a software QWERTY keyboard and other new features. Here's a list of some of the basic improvements coming from the update:

• MMS sees bug fixes as well as the new ability to save attachments.
• E-mail gets a large list of significant bug fixes including: new-mail notifications for POP3 accounts; new accounts are now set to check every 15 minutes (instead of defaulting to "never"); and there's also a fix to IMAP manually-created accounts so deleting messages works properly.
• The music player will now fade playback back in after suspending for a phone call. It also has a new media search function that allows for third-party apps to launch or respond to media searches based on artist, album, or title.
• The browser is seeing some significant updates, as well. Some of the new capabilities include: updated WebKit browser core; support for new, optimized JavaScript engine (SquirrelFish); copy / paste is enabled in the browser; find is enabled in the browser; and drawing has been sped up substantially. Pages with animations will load five times faster.
• With cupcake, Android will now support stereo Bluetooth.
• With respect to the camera software, Android will now support video recorder mode, allow for the sharing of videos, offer a list of video thumbnails, and permit local file playback.

Not bad, right? Unofficially, HTC indicated that Google, T-Mobile and HTC committed to bringing OTA updates to the G1 at launch. Google and T-mobile announced plans to add some of the features included in cupcake. Exactly which features will be added, no one is sure.

Officially, however, T-Mobile is not owning up to anything. A representative said in a forum post, "'Cupcake,' which is the code name for an Android software build, is still a work in progress that is considered to be a development branch and not for general availability. We will update you as T-Mobile G1 software updates are made available to T-Mobile customers." Basically, T-Mobile confirms that Cupcake exists, but isn't telling us anything more than that.

With Mobile World Congress around the corner, timing will be everything. HTC is having a press conference at the event, and speculation abounds that the company will bring forth its next Android phone, possibly even the "G2" seen earlier this week.