hello, i'm buying my first iPhone this weekend, (finally). it will be a iPhone 4s. i'm going to buy it on three on pay as you go. however, i want to buy another sim from three later which will be a 12 month sim only plan. i just would like to know - is there anything that makes it a 'pain' to change the sim in an iPhone? by this i mean - how will my iphone associate a new number/sim card with my same apple id/messages/imessage/icloud accounts? i intend to associate my apple id with my phone number on imessage so that messages on my mac works with my iphone and ipad/pods. any info on this would be greatly appreciated, i'm worried this will be a pain in the ass to do.