Tango has released a special version of their video calling app for the HTC Titan and HTC Radar. The HTC Titan in particular have been having issues with the app, with all system sound failing after a video call was made.
The bugs show the danger of system-level software which interact with the OS at a level beyond the usual sandbox which prevent such issues.
Hopefully the 1.1 update of the software, which is directed only at the HTC handsets, will correct the issue.
Tango for HTC v1.1 can be found in the Marketplace here.