Apple's next-generation iOS will allow FaceTime video chats over cellular connections, Apple said Monday. Until now, FaceTime has only worked over Wi-Fi networks.

When iOS 6 launches this Fall, having a cellular connection for FaceTime will be a welcome change for many users who don't have ready access to a Wi-Fi hotspot. But analysts question whether today's 3G networks could offer sufficient bandwidth to handle the live video coupling, or if 4G LTE being rolled out by the major carriers will be affordable when data plans are used to support FaceTime.

The 4G LTE being installed by AT&T and Verizon Wireless (and expected from Sprint this year) is about 10 times faster than their older 3G -- with average download speeds of more than 10Mbps. Meanwhile, the next iPhone is expected to support LTE when introduced later this year.

Apple's FaceTime over cellular announcement "implies that 4G is coming in the iPhone 5," said Ron Enderle, an analyst at Enderle Group.

Without LTE, a 3G connection with an iPhone 4 or iPhone 4S could be frustrating for users, since even Wi-Fi connections over FaceTime aren't always clear and sometimes don't have synchronous voice and video streams.

Wi-Fi data rates over 802.11n max out at 450Mbps, according to Wi-Fi.org. Many more commonplace 802.11a or 802.11g Wi-Fi connections max out at 54Mbps, still many times faster than the LTE being introduced in the U.S. Wi-Fi over 802.11b is rated at up to 11Mbps.

Even if the connection is fast enough, a cellular connection for FaceTime could be prohibitively expensive, as some users have discovered when downloading video clips or movies.

"I'm sure FaceTime will work over cellular, but the question is how well?" said Phillip Redman, an analyst at Gartner. Costs are harder to predict, he noted, unless a user has an unlimited data plan, like the one that Sprint offers, he added.

Having FaceTime over cellular "also doesn't mean that people will never use Wi-Fi again," Redman said. "I'd say the majority of use will still be on Wi-Fi."

Jack Gold, an analyst at J. Gold Associates, said FaceTime over cellular will "probably work...especially with LTE, although not very well with 2G or perhaps even 3G."

Gold was more concerned about the expense of cellular video chats. "With the carriers going to rationed data plans, what will heavy users have when they get their bills at the end of the month?" Gold asked. "Video takes bandwidth, even if it is highly compressed, and bandwidth is not free."

Apple hasn't defined how much bandwidth a typical video call will take, so "there is no good way to know what it will cost users," Gold added.

FaceTime over cellular "certainly [won't work out] if it raises people's bills" with carriers, Gold said.

Stories of exorbitant data usage bills for downloading video over a cellular connection are growing commonplace and AT&T and Verizon now offer tips and smartphone monitoring tools to guard against exceeding monthly data limits. They also send warnings to users when limits are exceeded.

Still, customers surprises could increase when FaceTime goes cellular.

One Computerworld reader who asked not to be named said she was surprised recently to get an $80 unexpected addition to her Verizon bill primarily for downloading a video attachment from a relative sent via email on her new iPhone operating over 3G. The video was less than 10 minutes long, she said, although she confessed she wasn't familiar with the terms of her new data plan or how she should monitor it.

Computerworld illustrated the data usage problem with video over Verizon LTE in December by downloading an HD 128-minute feature-length film to a Galaxy Nexus smartphone, which took up 3.7 GB of data. At the time, Verizon was charging $30 for 4GB per month at the time, up from the normal $30 for 2GB.

In addition to tools to monitor data usage, AT&T and Verizon also have some sage, if ironic, advice to avoid high data use over cellular: use Wi-Fi when possible. "You may want to use Wi-Fi when streaming video," Verizon said in a recent list of tips to its customers to help manage a data usage allowance.

It's advice that could matter for FaceTime-over-cellular as well.