In case it helps others, I called Ameritrade to ask about this. He said the voluntary deadline ends 22nd mid-morning, but he recommends giving verbal instruction to join the NOK party by Friday 18th. There could be a fee of $38 but for a reason that escapes me that would not apply to me. I asked what will happen if I do nothing, and he said he doesn't know. They could ultimately try to squeeze out old stock holders, maybe swap their shares with fair market value cash (which I'm guessing could be defined as a recent average?), or swap the shares anyway. He's not sure, what with them being French. The upshot is, if you plan to hold NOK, give verbal instruction by the 18th.