The US’ second largest ISP, EarthLink, is expanding its services from its basis dial-up base aggressively, particularly through its fairly new joint venture with South Korea Telecom, with which it will work on WiMAX and a cellular MVNO offering. Among the wireless services the partners will offer will be a dual-mode Wi-Fi/cellular handset, which will go into test phase next month. Included with the handsets will be a wireless version of EarthLink’s planned new VoIP service, which will also be offered on wired and wireless networks to its conventional base, especially as a broadband bundle to persuade users to upgrade from dial-up or defect from other providers. EarthLink currently offers VoIP service by reselling Vonage but will now build its…