Check the 3DS eShop or DSi Shop and you'll notice that Tetris Party Live is no longer available to buy, either in North America or European regions. We reached out to the publisher, Tetris Online Inc., for an explanation.
Casey Pelkey, vice president of marketing, had this to say:
I can confirm that Tetris Party Live is no longer available for sale within the 3DS eShop, effective 3/31/2012. Tetris Online Inc.’s license from The Tetris Company expired at the end of March and there are no plans to renew it.
As one of the few DSiWare games with online play, Tetris Party Live was a solid buy for many puzzle fans, but now 3DS owners' only digital option is the original Tetris on Virtual Console, sadly.
Update: WiiWare title Tetris Party will be available "for the foreseeable future" according to Pelkey.