[quote name='guinaevere']GuywithGun, 66 has been entirely correct in everything she's passed along in here and the warrant would very likely hold.[/quote]
Not really. Without any real indication that the phone conversations were sexual, there is no basis for the warrant. Assuming some idiotic judge actually granted the warrant, all the guy's lawyer would have to ask the police during the trial is, "Did you have any evidence about the content of the phone conversation?"
And the officer will respond, "It lasted a long time."
And the lawyer would say, "So you based your warrant on the fact that a phone conversation, in which you have no clue what was said, was long?"
Officer, "Correct."
And then the warrant would be ruled unconstitutional and every shred of evidence resulting from that original warrant would subsequently be thrown out, and the prosecution will have to throw the case out.
Trust me, in this case the police will actually have to:
a) Have some indication from the girl or the guy that the conversations became sexual in nature
b) Have consent from the parent to tap the phone.
In order to obtain a warrant from a judge, a police officer has to go through a lot of red tape and present a good amount of probable cause. Especially to tap a private phone conversation between two people.
And if you call a judge to obtain a warrant to tap a private line, and he asks for the evidence you have obtained. He/she will hang up on you when you say, "Well, we've heard that they've had some long phone conversations."
As I have said before, getting consent from the parents to tap the phone would be the easiest and best way to go. Consent to tap someone else's phone cannot be fought in court by the defendant. A warrant based on a long conversation would be thrown pretty damn quick.