@Shane Power,
What's it like managing a lot of houses? Just a giant game of wack-a-mole. You can fix everything, but something new will come up-- you just don't know when?! Or if a lot will come up at one time!--sometimes it's small/easy stuff, sometimes it's big stuff, it's always a surprise, and it's always expensive. lol One month i had a sewer line and HVAC had to be replaced within 2 weeks.
Outside of normal stuff, how many calls you get is inversely related to how well your properties are taken care. I manage 50+, and work a full time job. If you fix things correctly, and your house is in good shape-- tenants don't call just to call. Now, it's normal for stuff to have a lifetime, so if your fridge is 15 years old, you should be expecting it. I don't spend a lot of time on the phone, it's pretty simple-- they said X is broken, I call the person to fix X, and then wait for them to fix in a day or so. I'd say the majority of the tenants I only hear from once or twice a year. Nearly all my tenants are reasonable and easy to work with, so it's not that stressful. Just treat people how you want to be treated, and handle things quickly!
You want tenants to let you know of the problems! I always tell my tenants-- I like small problems, tell me when stuff is a small problem! I have our business phone on me 24/7, so essentially yes-- you are always on call. I tell tenants to call with normal stuff 9AM-5PM M-F, and emergencies 24/7.
You should have 2-3 plumbers/HVAC companies/roofers/etc to call if stuff breaks. Hope this helps!