Most of my customers are just using their existing router and matching it up with a mobile bridge like the Lucent MB8000. For private networks, such as VPN or MPLS, most failures occur at the local loop or smartjack. EVDO will provide a non-terrestrial backup to that unreliable loop. In the past, I've had to design my customers a backup network using satellite. Though, satellite still has some advantages over EVDO since it cannot be affected by local disruptions such as CO outages or towers. It also has very low jitter (I can provision VoIP over our VSAT service), and high speeds up to 2megs up and down. Plus, it can be used pretty much ANYWHERE that has the line-of-sight (i.e. doesn't have to be in a small wireless footprint).
As others said, EVDO is pretty darn secure... but I wouldn't call CDMA weak. I'm not sure how everyone else is rolling out their wifi, but at Verizon, it's not like tapping into a TDM or analog signal. Is there even a commercial device that can tap into CDMA? If you're using it to connect back to a HQ or whatnot, you'd definitely want a router initiating an IPSEC VPN and have a mobile bridge that will do VPN pass-thru. In order to eliminate this problem for MPLS-based customers, Verizon is planning on releasing EVDO backup direct to their MPLS network. No encryption needed (like we do with VSAT right now).