This is a bit of a generalization but, for the sake of argument, let's position the players in the Telco world as being split into two distinct halves: (a) the long-established mobile-centric operators such as Vodafone, Telefonica, Deutsche Telecom, France Telecom and so forth, and (b) the new entrants looking to break out from single service offerings (e.g. fixed-line) into unified comms.
Who has the upper hand? Who will capitalise on the promise of unified comms and win the battle for the customer?
The established players have infrastructure, they have years of experience in mobile (arguably the most difficult piece to deliver in the UC pie), and they have an extensive operational support structure. You could, however, re-phrase that last sentence to say 'they have many legacy systems in a complex architecture, they have years of experience but mostly limited to mobile, and they have an extensive operational support structure but little in the way of process automation for complex multi-service delivery.
The new entrants can bring a 'clean sheet of paper' approach to infrastructure (i.e. introduce a single, purpose-built system), they have broader IT-based view of comms in business, and they can introduce process automation as a way of reducing operational support costs. As before, you can put a slightly less positive spin on these statements.
It's a close call. The new entrants will be more agile and take a 'surgical strike' approach. The established players have the levels of investment available to be in for the long haul. As ever, it is business focus that will determine the outcome.