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26-03-2013, 13:07
Roaming SIMs which depend on callback systems run into problems in countries with very high population densitieis. Cellular providers typically prioritize outbound calls over inbound calls because customers notice failed connections on outbound calls first. There can be a million reasons an inbound call goes to voicemail. My sister was in Shanghai in November with a corporate iPhone using straight roaming and had problems with outbound connections.
If you are going to do VOIP Over 3g, I might try Skype in China. Skype is now legal in China and you don't need to worry about blockade running.
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