Is it silent, though? I got notifactions about it on my devices, then emails on each account. Then I went straight to delete the added numbers and disabled this "feature". It did not leave a good taste that I had to do this after the fact, I would have appreciated a notice with a chance to opt out first, because they may have already permanently stored those numbers in some internal history (I just asked Dropbox for my data and they listed every single email I've ever used on that account too). But, to be honest, I am not surprised, and I already consider all devices and numbers that ever come into contact with a Google account being permanently on record on some Google server.