It looks like T-Mobile is planning to show off its "latest and greatest" BlackBerry technology at an event on March 15th in Washington, DC. But if you're hoping for a some info on BlackBerry 10, don't get your hopes up — the invitation's BlackBerry OS 7 logo is a bit too prominent to assume it's going to be anything but something related to the six-month-old OS. Our best guess would be the launch of a T-Mobile version of the Curve 9380, which would bring an all-touch BlackBerry device to every major US carrier. We also wouldn't rule out an update to some of the BlackBerry OS 7 features, like Wi-Fi calling, which currently isn't as elegant as the old UMA-based standard.