Part of this depends on how you "really" want to unlock. If you want to recognize bluetooth connection from phone, there are a few that cover it like the Kwikset Kevo. I'd definitely lean towards models that still have a key funtion as well unless there's another inside entrance or the like. The downside of the bluetooth models is they work on detection alone, so anyone holding your phone could get in. If you can live with something that takes a little more input, look for something like one of the Yale Real Living locks with either Z-Wave or Zigbee, and combine with a controller. Samsung Smartthings is fairly cheap (and has a decent online community for customization and support). I use the Yale locks on my house, integrated to my alarm system, have been very happy with them. I can lock/unlock from the app, or use the code.
I actually use the SmartThings for my theater automation (it doesn't control the door locks or devices that my alarm does), and find it pretty easy to work with. You could easily set up a door lock with that, and have it either a) use the app to unlock meaning the person would need not only your phone, but how to get into your phone (assuming you lock it in some manner) or b) automatically unlock the door when it detects your phone on the wifi. That latter of course means any time you're home the thing would be unlocked.