I have been working on the same thing.
First, I would use the Mobile Controls. Round List and Rounded List Item will give you a nice iPhone like look.
I put a computed field in the Rounded List Item. In it, I have this JS:
if(document1.getValue("CellPhone") == null)
{
"Not Availabe"
}
else
{
"<a href=tel:\""+ document1.getValue("CellPhone")+"\">"+document1.getValue("CellPhone") + "</a>"
}
I have similar for things like addresses (actually they are a little trickier.
I hope this helps. Let me know if you have any other questions!
Bryan