Telecom (Jan. 2015)
Like T-Mobile, AT&T plans to offer calls that can seamlessly hand off between the Wi-Fi network and the LTE network. But AT&T hasn’t yet launched its voice over LTE service. Calls between the regular (non-LTE) cellular network and a Wi-Fi network tend to drop, which AT&T said isn’t a great experience.
http://www.cnet.com/news/att-plans-to-offer-wi-fi-calling-in-2015
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