The problem is: There is Vietmap available, what I did not manage to install yet. You can buy this software for 70 USD, sometimes the reduce it to 35 USD if you buy it with a new phone.
So I searched around and found Free Garmin. Someone said they might have the best maps for Vietnam. Might be, but when it comes to the cities, look at that list:
Hanoi (with Street names)
No Ho Chi MinhCity ????
Ok, next search result leads me to http://www.gps-navigation.at.tf/. again Garmin based, with now downloads to offer and not one single word about City Maps.
Lonely planet has a discussion about GPS and maps in Vietnam.
I found a nice workaround there:
I have a PDA based GPS but to get maps I've been scanning paper maps then using the Pathaway software:
to calibrate them and give me a moving map.
There are some maps on http://www.sjvietnam.org/map/, free for volunteers and internationl organizaions, made with a mapscanner. You need the www.oziexplorer.com software for this.
so, it seems only Vietmap is a sufficient solution. As their website is only in Vietnamese, I need offline help to go through. Will post my further experiences here...
.. to be continued