Last week rumours were floating around that Microsoft was to make the Mango beta release available to all Windows Phone developers via the App Hub. However, Brandon Watson, Director of Windows Phone development, was quick to debunk this rumour, saying that the beta was not due to be released last week.

News are coming in again today based on a tweet from Bill Cox, Senior Director of Communications at the Windows Phone Division:

[blackbirdpie url=http://twitter.com/#!/billcox/status/85960835133997056]

According to sources close to WinRumors, this "juicy surprise" refers to the Mango beta release, which is due to be available on the App Hub as soon as Thursday June 30. Neowin‘s sources also indicate that an announcement is due within the next 6-12 hours and the build number of the release is likely to be 7661.WP7_5_Trial. As reported last week, this beta will be available to paid subscribers on the App Hub only.

Sources from Neowin also said that the update process will be as follow:

[The update process is a] Zune software update and an executable that makes some changes to the registry to get the Zune software to look at the right place for the pre-release updates. It’s a series of two updates, just like NoDo.

The only guaranteed update path from this pre-Mango to the final Mango will be to revert back to the backup made by the pre-Mango update, since carrier-approved updates will only be made to carrier-stamped versions on the phone.

Of course, plans are always subject to change, so hold on tight for the next 24 hours. We’ll update you as soon as Microsoft make the Mango beta bits available on the App Hub. Stay tuned!