I will say this, it was nice when I used to work construction and had Nextel phones, I had a relatively featureless, scratched up, ugly brick of a work-issued phone that I used on the jobsite. When I left work, I would pop the SIM out and put it in my ic502 that I picked up for the sake of having a nice phone when not at work, which at the time I thought was awesome. Then I'd leave the work phone on the charger until the next day. I could see a lot of people who could utilize this such as needing to carry a phone but not wanting to endanger your $600 smartphone, so you pop the SIM in a cheapo flip phone for that time.
Sprint would have to put SIMs in cheaper phones for this to be viable though.