With the exception of corporate accounts, phone as modem has not been supported now for the past couple years. While the PAM service still works, the 9850 included, you must have subscribed to the service before it was decommissioned. I hope this helps!
Sprint does support PAM. Corporate Liable customers are able to use existing phones such as Blackberries with PAM. Individual customers have the choice of purchasing a phone that is hotspot capable, which is an improvement on PAM considering it can wirelessly tether up to 8 devices, depending on model, at a time. So there are options available for all sprint customers to be able to use their phone as a modem.
I previously was using a 8530 until last week when I upgraded. I had the option in "Change My Services" flagged to use Phone as Modem, but now I no longer have the option.
you must have subscribed to the service before it was decommissioned.