Wifi only is a neat concept, but the issue here is many hotels block the ports for Sling. This leaves 3G only. Very frustrating. Plus the speed of many hotel networks makes watching Sling (if ports aren't blocked) impossible.
Anyhow, I will never cancel my unlimited data plan for this very reason.
never had any issue in any hotel with sling. You might want to reconfigure you sling with a different port.