I'm not very familiar with the process since I always bought my phone from AT&T. My current Galaxy S3 has a micro-sim. When the 6P arrives I am going to need a nano sim. Can I order one in advance and then activate on AT&T's web site or do I need to visit an AT&T store when the phone arrives. Also is AT&T going to charge me an activation fee for the new SIM? If someone could layout how this is done it would be helpful - Thanks.