iPhone offers the same innovative features regardless of the wireless carrier you choose. If you choose AT&T or T-Mobile as your wireless carrier, your iPhone will use 3G cellular technology for voice services and either 3G or 4G LTE cellular technology for data services. iPhone can roam internationally on many GSM carriers around the world. If you buy iPhone with AT&T or T-Mobile, it will not work if you switch to Sprint or Verizon Wireless.
Apple announced its ninth-generation iPhones, the iPhone 6s and the iPhone 6s Plus, at a media event in San Francisco, California on September 9, 2015. The iPhone 6s and iPhone 6s Plus can be summed up beautifully with a single quote from Apple CEO Tim Cook: "While they may look familiar, we have changed everything about these new iPhones."
iPhone 6S and iPhone 6S Plus (stylized and marketed as iPhone 6s and iPhone 6s Plus ) are smartphones designed, developed and marketed by Apple Inc. They were announced on September 9, 2015, at the Bill Graham Civic Auditorium in San Francisco by Apple CEO Tim Cook , with pre-orders beginning September 12 and official release on September 25, 2015. The iPhone 6S and 6S Plus were succeeded by the iPhone 7 and iPhone 7 Plus in September 2016.