I avoid all the controversy by only using a pager at the live table
In all seriousness it depends on the house rules but I don't see a lot of issue with them being used by players who have already folded their cards but I guess it's how everyone handles it. In general I think people who are trying to collude are going to have a better system than sending a text saying I folded As 3d to another guy at the table, they would use hand signals and maybe a vibrating Morris Code receiver hidden somewhere in their persons.
I don't know how website blocking works but I would be more concerned with people trying to pull up GTO Wizard or something similar to know what they are supposed to open or defend with in their NEXT hand than people using a phone to blatantly collude over straight forward methods.
Just my thoughts tho I'm sure there's a huge amount of tools on both sides I'm unaware of and thus don't have a full picture of things anyways.
I would avoid playing J4o if you're worried about catching extra scrutiny in a live game, or looking down at your crotch too much.
Shout out to my girl Robbie Lew and throw shade at Mikey Postle