New to Android and very Confused

Hi All,

Im new to this forum and joined because I simply cannot for the life of me find an answer.

I have been a Virgin Mobile customer on an Optimus V for the past two years. I like the service but am in the market for a new phone. I was thinking if going with the Samsung Galaxy s2 but then t he other day in Walmart I caught wind of Walmart's Tmobile Glaxy s2. I was thinking that this phone may serve me better because it takes a Sim card and since I travel to Japan every year I could get a local sim when there.

Where I am confused is:

1. Is there a difference between the two phones. Sometimes I see Galaxy s2' s and they look totally different from one another. Also Virgin mobile offers a white phone as well.
2. Is the tmobile unlocked. Can one use it with an overseas provider.

In reality, I think maybe a Nexus 4 may serve me best but I need a hone in the next month and no telling when that be will be available.

Thanks,

Cfs123