In the Past Dish Tv Supported this feature,now i don't know, i am not using it .(Can record 1 channel & can watch other channel from same frequency channels)
with your word in D2h also does that in the past.
Tata Sky not even supporting recording in regular HD boxes except HD PVR boxes( can record 3 channels at a time- i think 3 tuners with single wire-price around 9000-9300 Rs).So it means you can record 3 channels at a time and can watch already recorded program at that time.
Airtel SD/HD DVR supports 2 channels recording (you can record 2 different channels and can watch already recorded program at the same time)-no supply now Airtel HD boxes, records 1 channel and can't watch other channel while recording (not 100% sure,needed clarification from seniors)
Sun Direct also allows only 1 recording at a time, not able to change to other channel while recording.