A system for transferring provisioning data related to a subscribed cellular telephone network for use in a user's mobile handset, comprising: one or more mobile handsets having an internal memory, wherein said one or more mobile handsets are configured to: access the internal memory for provisioning data; and use said provisioning data for sending and receiving calls from the cellular telephone network; a VSIM server having a VSIM processor, wherein the VSIM server is configured to be accessible by said one or more mobile handsets via a cellular telephone network; a VSIM database in communication with the VSIM server, wherein the VSIM database is configured to store provisioning data for use on the one or more mobile handsets and comprises a database of user accounts; an authentication server having an authentication processor in communication with the VSIM server; and an authentication database in communication with the authentication server, characterised in that the VSIM server is configured to receive user authentication information sent by one of said one or more mobile handsets via the cellular telephone network and a request to select one of a plurality of service providers; and if the user is authenticated by the authentication processor, the VSIM server is further configured to retrieve provisioning data associated with said one of the plurality of cellular service providers; and - transmit to the mobile handset, the provisioning data to enable the mobile handset to connect to a cellular telephone network of said one of the plurality of cellular service providers. one or more mobile handsets having an internal memory, wherein said one or more mobile handsets are configured to: access the internal memory for provisioning data; and use said provisioning data for sending and receiving calls from the cellular telephone network; access the internal memory for provisioning data; and use said provisioning data for sending and receiving calls from the cellular telephone network; a VSIM server having a VSIM processor, wherein the VSIM server is configured to be accessible by said one or more mobile handsets via a cellular telephone network; a VSIM database in communication with the VSIM server, wherein the VSIM database is configured to store provisioning data for use on the one or more mobile handsets and comprises a database of user accounts; an authentication server having an authentication processor in communication with the VSIM server; and an authentication database in communication with the authentication server, characterised in that the VSIM server is configured to receive user authentication information sent by one of said one or more mobile handsets via the cellular telephone network and a request to select one of a plurality of service providers; and if the user is authenticated by the authentication processor, the VSIM server is further configured to retrieve provisioning data associated with said one of the plurality of cellular service providers; and - transmit to the mobile handset, the provisioning data to enable the mobile handset to connect to a cellular telephone network of said one of the plurality of cellular service providers. - transmit to the mobile handset, the provisioning data to enable the mobile handset to connect to a cellular telephone network of said one of the plurality of cellular service providers.