a providers cell phone with her contacts. Can they use the text messages to prosecute clients?

And this is why I hate to read providers post OOps lost my phone..    
That info is dangerous in the wrong hands IMHO.

that at least upheld the right to refuse to give up your phone unless there is a warrant for it.

You can hope that the person had it locked down at least to make it harder for LE to get into it.

Still not a lawyer

...Unless you texted:  "Boy, that was the best fuck I ever spent $500. on in my life.  You're a great hooker!

 
There's a small chance that they may lure you into a sting by texting you pretending to be her but that's unlikely too.

A few years ago Phoenix LE was with a court order taking phones of arrested companions and setting up fake accounts on P411 and provide fake OKs for undercovers.

Please post any reference  threads links ect.... which discusses 411 being used in this way.. I haven't heard about this.
Thank you.

I am not allowed to post the link here, but I have a massive page on my old site (which I haven't updated in a few years) with zillions of quotes from emails from companions about the P411 legal situation from Phoenix escorts used with their permission detailing the LE use of P411. Especially taking over the phones and their identities after being arrested.    I hosted the Phoenix Private Email list for decades with about 1500 folks at its peak but has now been discontinued.  All the local boards shut down a few years ago with the AZ law that made promoting or assisting a felony in AZ.  Some folks may remember the old days and the sky-high condo meetings and parties I hosted in Phoenix

I don't have the citations in front of me, but I believe the Supreme Court ruling on this is yes, they can compel you provide a fingerprint (and by extension a faceprint) to unlock a phone but NOT a password.  The logic is that fingers and faces are external but a password reveal would be a compelled confession.  You might consider that logic twisted, but it is what it is.
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Use passwords and not fingerprints to lock secrets you don't want the government to see.

Regardless, of how you end up on the wrong side of the fence (ARRESTED). They still have to prove that the client actually put the cash in the Escort's hands. Especially since people love to through words/phrases around & have it mean something totally different then what other people could take it to mean.  It would be an extremely long process for the police to convict you (If you &/or your lawyer) know how to push the subject (Have huge balls).