Phil Schiller, Apple's SVP of Marketing, announced that the Wi-Fi calling support is coming with the latest devices from Apple. These would include the iPhone 6, iPhone 6 Plus, and other iOS 8-based iPhones. Wi-Fi calling will enable users to take advantage of Wi-Fi connections at home or in the office when a better call quality is needed in areas where the network is low. However, AT&T said that it is adding Wi-Fi calling support for its subscribers in 2015.

AT&T explains that the delay is caused by the company wanting to make sure that customers get a good experience when using the technology and that they wouldn't get annoying results such as dropped calls in between Wi-Fi and mobile data usage exchanges.

In the meantime, T-Mobile is providing support for the new feature when it launches. It addresses the issue by giving every subscriber a router that is designed to prioritize voice calls.

AT&T doesn't see the need to do the same because the company doesn't share the rival network's coverage issues. The company sees the upcoming feature as a complement to the device's voice over LTE and 3G and doesn't treat it as a replacement.

"We're very focused on making sure it's a great experience for customers, but we see it as a complement, not a replacement," said president and CEO Ralph de la Vega of AT&T's new Mobile and Business Solutions group as he spoke at the Communacopia Conference in New York City. "We feel good about a great nationwide network with unlimited talk and text."

Sprint also offers Wi-Fi calling but without handoff and not on the iPhone. Some mobile virtual network operators (MVNOs) such as Republic Wireless and Scratch Wireless offer services that depend wholly on Wi-Fi calling and texting.

BlackBerry, Android and Windows Phone are already offering a built-in support for Wi-Fi calling. When iOS 8 is rolled out, it would mean that all smartphones will support the feature.

Based on pre-order sales record, an AT&T spokesperson revealed that the demand for iPhone 6 and iPhone 6 Plus exceeded the demand on either the iPhone 5 or iPhone 5s when launched the previous year. This information may just give the carrier another reason to carry out the support to a feature which was announced together with the launch of the iPhone 6 models and the upcoming roll out of the iOS 8 in the next couple of days. AT&T must be able to ensure that its network can easily handle the situation when a user switches from cellular to Wi-Fi and vice versa.