A method and system for establishing wireless IP connectivity, in which a wireless communication device (WCD) obtains a routable IP address during its registration with a radio access network, rather than first registering with the RAN and then subsequently requesting and acquiring packet-data connectivity. Preferably, when the WCD sends a radio access registration request that triggers a registration notification to a home location register (HLR), the HLR or an associated entity will assign an IP address for use by the WCD and will deliver the assigned IP address in a registration notification response message to the RAN. The RAN will then deliver the assigned IP address to the WCD over the air in a radio access registration response message. The WCD may then use the assigned IP address to engage in packet data communications, such as to set up a VoIP session with another IP node, for instance.