I have alot of mobiles (iPhone & Galaxy) - I never sell the mobile I used, just store it into my old stuff!
Because 1st It's some kinda of hobby, 2nd and it's the most important >>> for security reasons
If you mean how many numbers using? currently I am using 3 1- Main (for calling) using my main apps/emails....etc 2- Whatsapp (I like to make my whatsapp separated "number and device" it's just personal way) 3- Virtual number from app store application (paid service)
Before few days, I was digging into my old stuff searching for something, and I found this box ;p