You can see it all on an app or website and transmits over wifi or cell network.

is there a good phone app?

You can scan the receipt with your phone using the QB app and it loads directly to the program.

However, if you're set on managing it yourself there's plenty of websites and apps you can utilize for rent collection.Some may or may not include messaging for requests such a repairs or maintenance, but if you're looking for rent collection there's quite a few options on the market that are affordable.

An app as well.

Then they have to learn a bunch of different other sites and apps, where each unit is, etc.

I have several keypad apps on my phone that I love, but if something goes wrong it would just be another headache. 

And that feedback is delivered via the OTA messaging app?

We have a guest app and guidebook through our PMS, but before that we made a Google Doc. 

Easy to use app, clear picture and it works at night.