I have used it htc wifi tethering 24/7 for years(all wifi tethering as before I used wmwifirouter)...*waits for applause..or boos whichever floats your boat*....
I'll tell you this, I have used ppc6700, mogul and a tp2 for tethering...
the overheating is caused by charging and large amount of discharging at the same time...a TP2 handles heat so far the best out of what I used..(TP2 I was able to get away with just placing it on a metal object and it keeps cool 24/7)
And yes I do mean 24/7 as there are days I don't get to sleep at all FML
If your gonna tether get a TP2..it should be cheap enough used and it definitely runs cooler then other phones..and just place it on any metallic surface..this will act as a heat sink for the fan...I tried this with mogul for example, the mogul needed a fan..it overheats too much..
The TP2 has a smart system to temporarily stop charging and the turn back on which is better on the battery...it gets bad when its 90-100 degrees outside and 100% humidity but thats what the metallic surface is for.
I couldn't be happier with a tp2 as a tethering device..well except it don't have 4g
