Believe it or not there is actually a way you can do this right now, full graphics and sound and everything, via an app called Splashtop Remote. Yes its another remote control program like Logmein or VNC so you'd need to have your SL PC running and configure some port forwarding if you want to access outside your local lan (although they have an experimental feature out in the latest release that does away with the port forwarding).
Now your SL PC will have to be decently fast to do this, but if you've got a PC that runs SL fairly well, you won't believe the performance you get from this. On my local lan I can move around with full graphics with almost no noticeable lag on my 1st Gen Ipad, and I hear its even better with an Ipad 2. It also works just fine tethered to my 4G T-Mobile phone, somewhat choppier but still very playable. I haven't tried it from a remote LAN but if it works on 4G I imagine it would be just fine on a remote lan.
More good news, as I said above it also forwards all sound to your ipad so you can hear SL music. I don't know if it works with voice, I have no idea if it forwards sound back from your ipad's mic to SL but I'd be interested to hear if anybody trys this. The best part is that its only around $5 or so (It may have gone up to $7 since I bought it), and you can get a free trial version that disconnects you every 5 minutes, so you can try it before you buy it.
Oh, it should also work fine on an iphone too, and there is an android version as well (although the Android version needs some work. It works, but its way behind the IoS version).
Good luck, hope this works for you guys as well as it does for me!
Cobra
P.S. And no I don't work for splashtop or anything, I just think its a very cool app and would like to see it supported so they keep improving it.