Back a year ago I noticed that an incoming circuit-switched voice call during a 3.5G HSDPA packet-switched data session forced the packet connection to go back to 64 kbit/s dedicated bearer while the call was ongoing. After the call the bearer was upgraded to 384 kbit/s but was only put back on the High Speed Shared Channels once the download was finished. Looks like the software on the network side has advanced a bit in the meantime as I recently noticed that even during a phone call an ongoing download continued at HSDPA speeds. Very nice!
Note: The test a year earlier was performed in the German Vodafone network while my latest observation is from the Orange France network. The RAN vendors might not necessarily be the same and it's even likely that they are not.