While the rumour has been that the LTE enabled 4.3inch screen, front-facing camera Lumia 900 would go on sale for At&t on March 18th, that date was never confirmed by either At&t or Nokia.
No word yet on a confirmed date as we are 2 weeks away from the unconfirmed March 18th.
I happened to email Nokia via their "contact us" page about storage capacity on the Lumia 900,
This was the email response I got:
Thank you for your email and for taking the time to write to us. Although we cannot discuss future plans with the Lumia 900 due to the fact that it is against company policy. I can tell you that the Lumia 900 links you to the Cloud, which allows for you to have unlimited storage space.
Glad to see you’re interested in the Lumia 900 and we hope you purchase one in April!
Best wishes from Finland"
FunFact: The Lumia 900 is Nokia's first 4.3inch LTE display phone (and the largest it's made till date)