To clarify you can still trade locally like always with 4th and 5th gen games. Pokebank is still going to work because its for the 3DS not the original ds - dsi. It's all the online stuff like the gts on d/p/p, hgss and bw1&2 that aren't going to work anymore.
Basically any game you own with the little blue Nintendo WiFi circle on the box, the online features will not work after 20th of May. Any game with the orange Nintendo network logo on the box is unaffected.