At this shindig in London, we expect Samsung to unveil the Samsung Galaxy S III — though where this smartphone sits in Samsung’s larger handset ecosystem isn’t entirely clear.

The Galaxy S III would be the successor to the Galaxy S II, which was never a single phone, but rather a line-up of devices with varying internal specs and exterior designs for different countries and carriers. Shoot, even the S II’s display sizes varied, with both 4.3-inch and 4.5-inch screens.

And while the Galaxy S II has been the flagship Samsung Android device for AT&T, Sprint and T-Mobile, the nation’s largest carrier, Verizon, has avoided the S II altogether. Instead, Verizon has gone all-in with the Samsung Galaxy Nexus, the first handset to boast the Android 4.0 operating system.

By all accounts, the Galaxy Nexus is currently Samsung’s best Android phone, its single-carrier limitation notwithstanding. But what will happen when the Galaxy S III is released? This question, too, is complicated by the 5.3-inch Galaxy Note, which has been a surprise hit for Samsung. More than 5 million Galaxy Note units have shipped worldwide — and this is a phone that runs on the horribly antiquated Android 2.3 (Gingerbread).

With Samsung making so many phones for different markets, carriers and countries, it’s difficult to figure out just where the Galaxy S III will reside in Samsung’s line-up, says Ross Rubin, executive director of the NPD Group market research firm.