We expected to know a lot more about Tango today, but information is still being revealed in dribs and drabs.
While the leaks have been filled with details like exporting of contacts to SMS and roaming features Microsoft has said very little.
Now the developer documentation on MSDN has confirmed that low memory 256 MB devices will not support background agents. These are 3rd party code snippets which run periodically (usually every 30 min) and allows downloading of information or uploading of data such as location. They can also be used to download data in the background and from the leaks this is ostensibly the reason why Microsoft has disabled it, in an effort to make their phones more carrier-friendly.
In effect however it means there are features which will just not work on some Windows Phones, and while we have been expecting this, it is unfortunate that Microsoft has not been more clear about the new features and new limitations of Windows Phone Tango.