I'm not sure how these subpoenas usually are worded specifically, but it doesn't seem like that contrived of a situation. Like, if you aren't the suspect and are ordered to hand over all devices used to communicate to <suspicious co-worker X>, if you have a separate device you just hand the thing over. If you hand over a personal phone, they are presumably going to bump into your walled off section and have some questions. Plus, you don't have a phone, while they are working on the thing, which seems like a pain.

This is assuming you aren't in a "hand over all electronic devices" kind of situation.

>> So you're saying that judge will ignore the separate profiles but it'll magically stop from depositioning all your phones that might contain work conversations?

Yes.

Source: Been subpoenaed three times and my attorneys have had restrictions placed on what can/cannot be searched... like I am assuming most competent attorneys can provide. The party has to have reasonable indication that relevant data is on personal devices so the opposing counsel doesn't go goldfishing through a bunch of stuff to turn up potentially unrelated dirt in discovery.