Before I got a smart phone it was dozens, now, less than 10, say 5.

Smart phones have only seemed to help in the process of dumbing down society.

I remember the numbers of relatives n friends -all- from BEFORE the cellphone era...some numbers are 50 y/o and I have not used them in decades.....BUT the "post cellphone era numbers" are a mystery to me. LOL
I know my number

I know my own number and only one other.

Just my wifes.... I'm screwed when I loose my phone. I loose everything. It's sad but true.

Not a single one. I am not that important neither are they to be memorized. I know where to get the number from. I got this device called notebook and with a pen interface I had recorded the numbers for posterity. My mind has other priorities to handle.

I thought I knew more, but now that you've asked, I can only recall the numbers for my two sons, my mom and a few numbers at work. I do remember my grandma's number still, and she passed away 13 years ago.

About five personal and 10-15 at work. I have had a knack for memorizing numbers if I use them often by dialing, writing, calling them out verbally etc... Maybe I should set my gazillion passwords that way!

I know 3 people by phone number and my own.

I've only got my own number, and my aunt's, memorized. Although, I do still remember the phone number of house I lived in when I was a kid.

I only know my mothers home phone number off by heart, as she has had the same number for 20 years +. It would be a giant fail if I lost my cell phone, but there is always facebook and the interwebs to get peoples numbers again.

Though anyway back in the olden days when we had no cell phone, was that not what address books were for? What happened when you lost that! ?

Only remember a few...