Does Sprint roam on Verizon

[Bruce39]

I thought Sprint always "roamed" on Verizon network. Last week in the mountains of Colorado; both me & my sons business phone (both Verizon) had great service (4 & 5 bars). His personal phone (Iphone 6 on Sprint) could not connect - had "no service"

 

[Almeuit]

In some places yes. They have to have a roaming agreement in place for the area.