We recently heard how Sony was looking to claim the number 3 position in terms of worldwide Android sales. The catch, at the time they did not offer much in the way of specifics. While they haven't revealed all of the plans, a recent Reuters report does have Sony CEO Kaz Hirai talking about how they are looking to achieve that goal by going through Europe and Japan.
Notably missing here is the US and China. According to Hirai, Europe and Japan account for a collective 60 percent of smartphone sales and based on that, they are "the most important areas" for Sony. Further chatter from Hirai includes how they plan to "put substantial resources there" and how they are "not yet" looking to move into the US because "it's not realistic to try to do everything at once."
There wasn't much further given in terms of when Sony may start pushing harder in the US (or China) and Hirai simply mentioned they will "start gradually." Keeping on the topic of the US, the carrier availability is quite limited with T-Mobile being the only real option. There are however, unlocked handsets available. But as we often see, they hold less of an appeal to the average customer.
Sony does have some strength in their home market of Japan. They are currently ranked second, behind Apple and it looks like the competition between the two will continue. NTT DoCoMo, which is the largest carrier in Japan has focused on the Xperia line in the past, but they also recently came to an agreement with Apple and will have the iPhone available.