AT&T may be experimenting with innovative ways to build a more economic mobile network – from virtualization to millimeter wave to powerline (see separate item) – but it is also heavily focused on driving down costs in its conventional platform. Small cells, and better deals from macrosite owners, are the key. AT&T was once the most bullish of US carriers about small cells but has been more cautious recently about sharing firm figures. However, Bill Smith, its president of technology operations, told last week’s Pacific Crest technology leadership forum that small cells would be vital to AT&T’s strategy, especially as it moves into high frequency bands, which only support short range base stations. Smith said: “If you look at some…