Maybe I'm innocent in always using my ordinary phone and not a specialised punting phone, but is there any problem if I'm not in a relationship?
Depends. Think of these few things and how you would feel about them.
1. She chucks your number on the likes of Saafe with some drama queen type warning she has fabricated, or claiming you are a timewaster. One of your real life friends for a laugh googles your number and finds that review and that you have been seeing prostitutes (friends do this you know when bored).
2. She sends a random text, or phones up your number at 7pm at night for random reasons. i.e to tout, or a wrong number. Or she is upset over something you have said on UKP and phones up to have a screaming match at you out of the blue. When you are with your friends or family at the time.
3. She leaves voicemail messages on your phone for whatever reason which you play back when with your friends/family etc.
4. She loses her phone with your contact details stored in there and the next person does crazy stuff as they twigged on it was a prostitutes work phone they have found.
5. You have your phone tied into your facebook account and she chucks it into their as password recovery and then finds your real name and email address from that (Facebook does that you know, if you go to password recovery and put the phone number in, it gives you the persons real name and a large portion of the email address and often its easy to guess the rest).
6. You have your phone number on the net for innocent reasons (Part of your job, or you are part of a club etc) and the WG googles it and finds all info on you.
7. You have whatsapp tied to your number, and a photo of yourself on whatsapp. And she gets to see it by adding you number to her contacts.
There will be many more, but that is 7 to consider to yourself.