Yeah, it sounds like you'll be able to use the uAvionix network the same way I use my Stratux network, and your phone and 740 should sync just fine.
I'm not an iOS guy, so others can correct me if I'm wrong, but I'm pretty sure you won't be able to connect your phone to both the uAvioncs network and the cell network for data at the same time. However, that may not be too big a deal. On my Android phone, if a (known) wifi network is available, it will preferentially attach to that and try to use it for data, so if I were in your situation, I would turn on wifi when I wanted to sync to the 740, then turn wifi off when I wanted to use the cell network for data connections. If your iPhone works similarly, then that may be an easy switch for you, too.