My take: 4G gear is now cheap enough it's time to stop building 3G except in the poorest countries. 4G is so much cheaper to run essentially every telco in the developed world is quickly migrating. That's a very good thing because carriers inefficiently using spectrum limit everyone's capacity.
China Mobile is proving it also make sense in less affluent countries. They have about ~140M LTE customers today and are adding 15M/month. They expect 250M by year end 2015.
A year ago, 4G phones cost $50-100 more than 3G. As new chips came out and competition developed, the gap has narrowed. Spreadtrum, 20% owned by Intel, say their new chips will bring LTE phone prices down to $65 or so.
Depending on how you measure, 4G LTE delivers 3 to 10 times as much capacity as 3G. (Using MIMO and carrier aggregation.) On a wall street call, a Verizon executive estimated 4G cost 70% less per bit delivered than 3G.
Adding 15M 4G subscribers per month, China Mobile is on track towards its goal of 250M 4G subs by the end of 2015. That overwhelms the results at both domestic and international alternatives. About six months ago, CM passed early leader Verizon (< 100M, I couldn't find a precise figure.) Yearend 2014, they had built 600,000 base stations and had 90M 4G users. That's about 3x the density of Verizon or AT&T's network, adjusted for China population being 4x the U.S. 400,000 more basestations are expected in 2015, topping 1,000,000. Fiber home is also coming strong in CHina.
TD-LTE phones are not that much more expensive than 3G phones.