The fundamental problem is that AT&T is too big now for its own good. Everyone -- including AT&T's own shareholders -- would be better off if the federal government broke up AT&T again... but THIS time, into AT&T Wireless and U-verse, with their fiber, ROW, and trunk lines held by a third company as a co-op jointly owned by ATTWS and U-Verse (so ATTWS couldn't stop U-Verse from aggressive expansion, and U-verse would HAVE to aggressively expand to remain relevant & profitable).
The hard part would be structuring the third company's charter to ensure that AT&T Wireless and U-Verse both had the right to lay their own fiber within their shared ROW, and could fiber connectivity to others without being able to limit the other partner's ability to do the same. So U-verse could sell fiber to Sprint & T-Mobile, and AT&T Wireless could sell fiber to Comcast, even if neither one would willingly sell fiber to their "partner's" fiber customers.
IMHO, making the third company truly independent (instead of a bitterly fought-over co-op between the two new AT&T fiefdoms that neither could truly control) would be a mistake on par with Britain's Railtrack experiment. When you have one company that only owns bulk infrastructure, its main incentive is to spend nothing and wring every bit of equity it can from it while running it into the ground. On the other hand, if there were two companies at each other's throats (AT&T Wireless and U-verse) with every tragedy-of-the-commons incentive to overbuild & try selling surplus capacity to others, that's exactly what's likely to happen. And when it comes to fiber, more == better.