They haven't told me of any conversion... yet.

This would entail new CC #'s for everyone who held the popular Continental Airlines Card, which became the United Card but still issued as a MC for the millions of Continental Card holders. That is a lot of customers, a little hard to believe.

Wells Fargo, the "founder" of MC, did the same thing about a decade ago. No exceptions, every single MC credit/debit/ATM card for existing WF customers got switched to Visa. It was a mess and a huge PR disaster, as newspapers wrote stories about all the customers whose autopays started getting rejected because the CC # had changed.