To be honest, the 3GS, the 4 and the 4s were never used by me as primary phones. I came in with the iPhone 5, and that particular iPhone 5 in the picture is actually the fourth (and final) replacement of the original.
The 4 I got from someone on Reddit for $20. It was missing the two screws by the connector, which were easily replaceable via eBay.
The 4s is 8GB, and was my son's first cellphone. I got it for $25 from a member here for my son's birthday. Tracked down a box, stickers, cables/ear buds/power brick and documentation off of eBay for him. He did really well with it so I got him an iPhone SE in 2017 for his birthday and I got the 4s back for myself.
The 3GS I got for $20 off eBay a year or so ago to replace the 3GS my sister originally gave me in late 2011. I had sent her phone off with a friend who needed a phone.
The 6s+ was my primary from 2015 to 2019 when I got a my Pixel. We (my wife and I) got our current primary phones, the 11 Pro Max last year (Feb. 2021).
Like you, I don't sell my old phones.

I just move them on to other uses. Which reminds me. What you can't see is in the original picture is an HTC Touch Pro. This one (below) is a replacement for the one I had from 2009 to 2012 when I got the iPhone 5. My original had been sent off to another Sprint user who needed a new phone at the time. I use the replacement primarily as a desktop clock now. It's on my WiFi network though so I can access it via VNC if I want to.
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