Cisco calls DISA "Mobile Voice Access." In CCM 3.x and 4.x it required a separate Mobility product and server.
In current versions of UC Manager, this feature is built in and only requires a VoiceXML-capable gateway running H.323 or SIP. This can be your existing voice gateway as long as you have sized it correct and are using H.323 or SIP for signaling. MGCP will not work as it does not support voice applications.
http://cisco.com/en/US/docs/voice_ip_comm/cucm/admin/7_0_1/ccmfeat/fsmobmgr.html#wp1203108
MVA is explicitly enabled on a per-End User basis.