You can't buy a 911 block, You'd have to modify an existing block, I know, I Tried.

And, there are Landlines, Arrithemedavies. Not all of us have cells. The old DTMF/ centrix "dial" system still works. I have no cell, one of my (still Working) phones is a 1918 Western-Electric wall phone with a Crank.

Nothing at all : "illegal " about blocking any number on Your phone. Might, just might, be a law against manufacturing and selling specific 911 blocks.

I worked at 3 co's that made phone eqt, including Harris DTS for 8 years. This is what I was told by Engineers.

If you mean attempting to block YOUR number from appearing when you call 911, you CAN'T.

Note: Calling 911 IS calling the police.

911 wouldn't call you so how can you block it?