In the race for more and more spectrum, it was not surprise that both of the most promising sources of wireless capacity – unlicensed bands and high frequencies – were prominent themes at Mobile World Congress last week. The US may have been uncharacteristically ahead of the game in deploying LTE, but its spectrum policies could hardly be said to have been equally ground-breaking. Most first wave 4G has been rolled out in spectrum which was acquired and run in the traditional way – long term, exclusive licences in sub-3 GHz bands, bought for huge sums at auction. But in recent times, the US is becoming a leader in new thinking about spectrum too, both for expanding 4G services and…