UMS protocol on Android Tabs I'd like to have a android tablet on ics which allow UMS (usb mass storage)

I saw that some of the current models didn't propose UMS (like galaxy tab 2 or google nexus), only MTP. It sounds like a problem for me because I have to retrieve the file programatically from a c# application.

do you know some models compliant with UMS ? or a way to activate UMS on my already bought Galaxy tab 2 10.1'.

Regards
Instead of trying to get something to work on the tablet, that doesn't by default, I would suggest to look at how to retrieve the file over MTP with C#. 

MTP allows the internal storage of these devices to be formatted to a native linux format, like ext4, instead of FAT32. If you were able to get UMS working, chances are you wouldn't be able to mount it in a windows machine because it doesn't know how to handle ext4. This allows the android OS to actually handle how the files are written to the storage. 

MTP is also a safer protocol because it doesn't "mount" the device like an actual drive. So there is less of a chance to corrupt files or the disk if you just unplug. Mounting via UMS also makes that storage unavailable to the Android OS which could cause other concerns.

There are lots of models of tablets that still support UMS, but most of the "current" ones support MTP because it is a safer way to handle the storage. IIRC, devices that do not have an slot for external storage will not (should not?) support UMS. And when they do, only the external storage will be mountable from the "Client OS".