Where have you heard that March 18th is fact? You said earlier (or someone did) that the media is reporting it as fact. Everywhere I've seen it's being reported as "rumored date" because there hasn't been an official announcement yet.
Yes, some (NOT ALL) have put a question mark in their headline, some have even put the word rumor in the headline. Many, many others have not:
CNET headline: "AT&T to offer Nokia Lumia 900 for $100 on March 18"
WPCentral headline: "Nokia Lumia 900 set for March 18th and only $99"
BGR: "Nokia Lumia 900 launches March 18th for $99.99 on AT&T"
There are DOZENS of articles that state it as fact in the headline and many that say March 18 or March AS FACT.
If Im NOK, I dont let the press set this expectation. You need to step in and set the expectation properly with your customers. If it was still TBD when this rumor hit, then just say that within a week or two of the rumor starting. Yes, you like the hype if you're NOK; as a matter of fact, you like that they're writing at all. But there's a line. You dont let the press and others take
your ball and run wildly with it. You need to take at least some action to control your key expectation set. That's features, pricing and timing. It's too late now for me. Im already po'd. I really hope they dont say anything through the 18th and some people show up (or better line up) at AT&T only to be told..."sorry, no phone. maybe next week".