Sprint used to only do analog roaming even on compatible digital carriers. The
theory I've heard is that it was to discredit the other companies by pointing
out that when you roam on their networks, you had an analog signal that was
inferior to their digital signal (this was back when they started marketing
their PCS service). They are now doing digital roaming in some places, and I
imagine they'll have to add more and more as other carriers stop upgrading
analog networks, but right now in Southern California, you roam analog where
there's no Sprint signal (I'm told it's on Verizon).

Does your friend keep his phone's PRL up to date?  PRL's 10024 and 10025
 added much more digital roaming and changed the priority in many
roaming situations to prefere digital roaming over analog.  If your
friend's phone has a PRL older than 10024, it is likely to prefer
analog.  Look thru the phone's menus for a 'display...version' or 'phone
info' menu item that shows the PRL version.  See the recent thread
called "Downloading PRL" for info on how to update a phone's PRL.

To roam on Verizon's CDMA network you need two things, A phone capable of
digital roaming at 800mhz CDMA and a prl entry for that network. Your
friend probably does not have a tri-band phone and is only capable of
analog roaming on AMPS at 800mhz and digital roaming on 1900mhz CDMA. Keep
in mind Verizon's native network is almost always 800mhz CDMA while
SprintPCS' network is 1900mhz CDMA.

    Maybe verizon charges more for digital roaming than amps roaming.