Tuesday, December 23, 2014

When marginal price of a call goes to zero


Having an unlimited mobile plan is a very nice thing - you do not need to worry you will pay more than you expect for using your smartphone.

Also, at some point (often quite early in a month), successive calls become free.

Or to be precise - the marginal price of a call goes to zero.

Still, I was wondering, how much of the unlimited am I actually using.




nju mobile is one of the Polish mobile operators, offering unlimited plans combining voice, data and SMS/MMS (the last I am hardly using).

I downloaded connection data for the last six months (178 days to be precise) and wrote a simple R script to analyze it.

Over the last six months, I was using approximately 300MB data per month (1.7GB in total) and made 204 phone calls totalling roughly 2,000 minutes, or some 330 minutes per month (the average call time was 11 minutes).

I did not notice any clear trend in my monthly usage.


I was especially interested in my data transmission, but it seems that even if the intensity can vary significantly between moments, the tendency is quite stable.




Naturally, I am not talking all the time :)

I'm usually calling between 7 am and 11 pm, with the highest intensity around the noon.


However, the length of a call can very significantly.

> summary(voice.call.length)
    Min.  1st Qu.   Median     Mean  3rd Qu.     Max. 
 0.01667  1.71200  6.10800  9.63700 12.89000 69.72000 


The majority of my calls are below the average (~10 minutes), but there is a long tail, too.

Call recipients had different characteristics (average expected call length and call length variability).


In connection with the information whether I had called a recipient before, it should be possible to predict the call length.


There are other factors, such as:
  • day of a week
  • time and length of the previous call with a given recipient
  • preceding calls
  • etc.
that may be used in the call length predictive model.

But that is a task for future, when more data is collected :)