I have no experience on this at all but I think it's a pretty neat idea and a good way to conserve space. I've seen some pictures online of people doing this to fig trees.

heat might be a problem here especially if it's along the wall of the house, but if it's on a wooden trellis it might be better?

This is an idea I've been toying with. I have a very small yard, and because my neighbors have a lot of mature trees, only a limited amount of it gets good sun. Naturally, the largest sunny planting area I have is a long west-facing block fence. I've been thinking of putting grapes along there, and possibly apples, although I was told that apples would likely fry in the summer heat. I'm tempted to try anyway, since we eat a lot of apples, but maybe I'm crazy!

You can grow apple trees here, a friend in Arrowhead has two trees. I think you need two for pollenation. Check out RSI Growers

Here is a link that might be useful: RSI Growers

Yeah...it's the espaliered on a west-facing block wall part that I'm not sure about. I would like to try Pink Lady and either Gala or Fuji; they are supposed to be good pollinators for each other.

I wish RSI Growers were closer to Tempe, I'd love to go out there and take a tour around. Everyone seems to have very good things to say about the place, and it would be great to pick the brain of someone so knowledgeable.