Nowadays, cellphones are becoming a necessity. This necessity, plus the resulting demand has made cellphones even cheaper. In my landlording experience, there are two real instances where cellphones are particularly effective.

Showing the Units
Applicants who are apartment hunting are typically of the profile who can afford cellphones. When they look at the apartment site and decide that it's a possible find, they'd usually yank out their cellphones and inquire or ask to see it. Now, I normally wouldn't just run over to the site and show the units. I'd rather want to know more about these applicants first. A mandatory requirement is them having a ready checking bank account. Corz, if I get to learn more, all the better. If I hear or read via sms text how arrogant they are by the way they communicate, then that's a peek into their personality. It's easy to identify red flags in many cases. It is convenient for them to just call me, as it is convenient for me to quickly weed out undesirables. With this quick communication, where I may be reached virtually anywhere, I could easily determine if its worth my while to run over and show the units.

Apartment Maintenance
How I wished that ALL people had cellphones INCLUDING contractors. By contractors, I refer to carpenters, welders, electricians, plumbers and all handymen.

In hindsight, this particular idea or article may even be rendered "irrelevant" as cellphones become commonplace and will simply just be THE defacto manner to communicate with anybody.