AT&T is expected to benefit the most from the launch of the iPhone 4S in the US, according to analyst firm Kantar Worldpanel ComTech. The company says AT&T still holds 84 per cent of all Apple customers in the US.

More than a year ago, the launch of the iPhone 4 helped AT&T overtake Verizon's leading position in the smartphone market, increasing its share by 11 per cent in the first quarter (Q210 vs Q310).

Since then, smartphone sales on AT&T have suffered, both from Android's growth on competing networks and from AT&T's loss of exclusivity to Verizon, causing the carrier a significant loss in market share.

"Despite AT&T losing exclusivity on the iPhone, 84 per cent of Apple's customers are still connected to the carrier, and of these, 44 per cent have had their Apple device for 18 months or longer and would soon be ready for an upgrade," says Lara Biddiscombe, global account director at Kantar Worldpanel ComTech.

"iPhone customers are very loyal to their brand; Kantar Worldpanel ComTech's panel shows that only 8 per cent left the brand over the past year, and carrier loyalty is also high, with only 7 per cent of AT&T customers leaving the carrier over the past year. All in all, AT&T is very well placed to capitalise from the release of the iPhone 4S."