The fixes to CE 6.0 R2 VoIP will be included in the July 2009 QFE package which should be released this week.
These QFE's are a direct result from the support incident we opened with Microsoft regarding this issue. The support incident was of course completely free because this was a bug, so, whenever you find a bug that needs fixing: Please open a support incident with Microsoft and help make Windows CE better!
At this moment the whole Windows CE support procedure you have to go through is frustrating to say the least, but Microsoft is updating its support procedures for Windows CE so it will be streamlined in the near future. For now, just keep your cool on the phone and follow the instructions as per the leaflet inside the Windows CE 6.0 box. Do not pay or give them your credit card number if you still have a free support call left (you get 2 free support calls when you buy Platform Builder for Windows CE 6.0).
I'll keep you updated when I hear something back from Microsoft regarding the support procedures.