One thing that you all may be overlooking is that you have to take a phone with you as when you get to her postcode area you then normally phone up say i'm here, then she will give you the house/flat number. So unless your parked very close by, never a good idea, you have to take the phone into her place with you.
Now if alls well then fine and I get into the habit of checking I have my car key, just the key nothing else on that ring, and my phone.
Now what if its a bait and switch and you walk what if your drop the phone what if its a very adverse situation where you have toi do a runner what if its such a good punt your big brain has been mesmerised by litle 'ole brain, and your phone has slipped out of your pocket it can just as easliy slide out and gone under the bed.
So now your outside her flat ringing her doorbell whilst shes in the shower or maybe you've only just noticed it go when your back to the car? Shes now with another punter. So it may be quite some time before you can get to her place and you can't now phone her. Lets hope it isnt the missus phoning her either:(
It once happened to me an I had a bit of a job getting the phone bak this was only a cheap Nookia phone I can get them for what 10 quid odd at Tescos?
And its a totaly anonomous paid cash for the phone, cash for the top ups, totally untracable and I remember to flush out any numbers and texts when the punt is over and it does live in the car its the backup phone in case of need if the other one devlops a fault or has a flattened battery etc Worked fine like that for years:)