How long do smartphone makers usually offer/sell their flagship phones?

[N YFB]

Just curious, because in the past I have seen smartphones I was interested in stop being sold and discontinued just as I was ready to buy one. Is there some sort of unspoken rule these phone makers go by, like fiscal year or financial quarters in which they cease producing last years phone? About how long can you expect to buy or pick up a company's flagship smartphone before it is no longer available through mass market channels or through the phone maker itself? How do you better predict when a maker is going to switch to a new phone and stop manufacturing and selling their current flagship?

 

[Rukbat]

There's no way to predict it - they usually schedule a production run that could last anywhere from a week to 6 months - then, when the stock runs out, it runs out. Flagship or not, the production is about the same, it's only the updates that continue for 2 more versions with a flagship phone.