Would I get into trouble if I hand in a "stolen" phone which is mine to the police?

Did you have these conversations in person or online/over text? If it was online/over text then you have evidence she's talking **** so don't worry about it.

That is also something I forgot to mention. The argument was in person but there was also texts back and fourth, there was some arguments on texts as well but no mentioning of reporting the phone stolen.

You said you'd send her the monthly phone bill, have you done this?

Yeah, the full amount has been sent to her via bank transfer each month, same date.

At Christmas my sister decided to get me a new phone. I didn't really need one as my old one was and is working perfectly fine and it's only three years old. She still went ahead and brought a new phone in her name on contract for me, I told her I'll send her the monthly phone bill money.

We've had an argument, she said she's going to end the contract and report it as stolen. If I hand it in to the police after she reported it stolen would I get into any trouble? We're not on talking terms, we've blocked each other on everything, it was a really bad argument as well.

Unless she's accusing you of stealing it, then it's extremely unlikely the police will investigate this; all she'll get is a crime reference number so she can claim on any insurance policy.

Simply put, police get hundreds of phone / bike thefts every day, and it's impossible for them to investigate all or every reported case (well not without taking valuable resources from other, more important cases).

On the other hand, if she does accuse you, then make sure you've got some proof that it was a gift and the arrangement you had then they'll throw out her case along with the leftover Macdonald's they've just had. Sufficient evidence could include:-

1) Any written details /documentation of the contract (e.g. letters)
2) Any Christmas cards / messages that reference that she gave the phone to you
3) Bank statements that show you paying for the monthly phone bill you described,

IMHO, the main thing you want to do now is make sure you've backed up all your personal data from the phone, in case she decides to remotely block or wipe the phone (which she could do if she's not taken seriously by the police).

Just a quick update. I managed to track down her place of work today with the help of google search. Whilst I went to town I popped to my local royal mail and posted the phone to her place of work with her name on so hopefully sorted now. Did back up my data and factory reset the phone.