In addition to support for lower-end specs, a few of the features that Tango is scheduled to include are the ability to handle SIM contacts and to send multiple images via MMS. It is presumed that there will be additional features that will be detailed by Microsoft once the update receives its official announcement.
Chinese site, WPDang, is reporting that the Tango rollout will begin as early as this month. WPDang also says that Microsoft's intentions are to update 90% of the currently available Windows Phone handsets to Tango by the end of June.
If that report is accurate, we should hear from Microsoft very soon about what we can expect from Tango.
source: WPDang via IntoMobile