I have been living out of suitcases for a few weeks with very little access to the Internet. So I have managed to test two iPhone clients for Second Lfe.
The one I have liked in Touch Life from Pocket Metaverse. The experience you get of Second Life is pretty primitive. The key feature is you can see which of your contacts are online and IM them. You can also see where you are on a map and even move about kind of crudely.
So using Touch Life you can IM friends. You can go to events and participate in the Chat. And you can move your avatar about using a crude tool.
But you can not see anything below the map view. You can't change clothing or interact with animations. You could probably go to a lecture but not a dance. VoIP is not currently provided.
The popular Sparkle from Genkii provides only IM features. Sparkle is only a IM tool and does not allow you to see the map. The tool does have a cool "sparkle" sound and buzz when you get an IM and is probably a good basic tool for just staying connected.
Touch Life offers more features but the added features don't give you much. You can see your inventory but you can't put iteams on or rez them. You can look at land marks but not teleport to them. You can go to places but not see them or interact with them.
Still looking for a tool the allows better interaction on a iPhone scree.
But I would notice that I now have 7 different SL browsers between my computer and iPhone. I have the LL SL browser 1 and 2, the emerald browser, Hippo and Dale's 3D viewer.