The T-Mobile G2X is available for purchase now on T-Mobile.com and if you get in before 5 p.m. Eastern you could still pay just an extra $25 to have it delivered right into the comfort of your own home tomorrow (or $12 to get it Monday). Either option would net you a couple days of gloating with your new toy before just anyone can walk into a T-Mo store next Wednesday to fondle this dual-core beauty.
According to some T-Mobile forums there were issues getting the orders to process immediately after the G2X went live, but those have since been straightened out so it should be smooth sailing if you want to get your order in now.
For those of you that might be worried about the potential post acquisition future remember that the G2X is one of the devices that has you covered even if/when AT&T repurposes the existing T-Mobile bands. Beyond that the G2X is one of the most future-proofed smartphones available at the moment with a Tegra 2 processor, 1080p video capture, and a 1.3 MP front facing camera all running on stock Android which should hopefully mean a quick update to Gingerbread and beyond.
If you are looking to stick with or convert to T-Mobile despite the impending acquisition by AT&T the G2X has to be on your very short list for purchase this Spring.
Update: Knslyr in comments shed some light on the discrepancy in shipping options some of you are seeing. You will only see the Saturday and Overnight shipping if you are a buying the phone with a new line of service; apologies to the existing customers looking to upgrade I guess. On a more positive note orders with standard shipping have been getting a 4/18 delivery date.