On December 21, 1999, Sony launched its first digital audio players, under the name "Network Walkman" (alongside players under the VAIO name). The first player, which used Memory Stick storage medium, was branded as "MS Walkman". Most future models would use built-in solid-state flash memory. In 2000, the Walkman brand (everything ranging from cassettes to the Memory Stick players) was unified, and a new small icon, "W.", was made for the branding. Later, Walkman-branded mobile phones were also made by the Sony Ericsson joint venture.