I have an iphone 4 from at&t, which they unlocked. I would like to test out straight talk service, while still keeping my at&t service. If I put in a straight talk sim card, I understand I have to use an apple program on my laptop to add a new apn profile, or use the unlockit website. Once I put the straight talk sim in and change the apn settings, if I then go back to the at&t sim card, do I have to download a new apn profile or will at&t automatically download it to my phone? Thanks.