EE's forthcoming VoWi-Fi service could face delays after the operator admitted the service "isn't working well enough" in trials, due to the complexity of the technologies involved.
The native service is planned to go live by the end this year, ahead of a launch of a VoLTE service in 2015.
But the UK operator's Director of Network Services Tom Bennett, told Mobile Europe: "My intent is to launch [VoWi-Fi] in the coming months but I will not launch an inferior product for the sake of hitting a deadline. Currently it just isn't working well enough. There's 25 years of voice to reinvent onto an IMS infrastructure."
He said engineers were having to contend with 17 extra systems. A key challenge is how to deal with making traditional circuit switched networks work alongside newer IMS networks across 2G, 3G and 4G.
Bennett explained: "We are tuning up voice again and from an engineering perspective, there's 25-30 years of stuff that we need to go through again... that's quite a challenge."
Other operators have gone down the route of releasing an app, which Bennett admitted would provide a workaround but at the expense of a handset's battery. He said: "If you go with an app, it's easy."
Bennett described the project as the most complex project he has ever worked on when Mobile Europe visited EE’s test lab earlier this year.
The Director of Network Services was more positive about another key technology. He said EE expected to launch carrier aggregation by the end of 2014 in London, with it hitting other city centres in 2014. The operator has been trialling the technology in the Tech City area since late last year.
"The reason we are doing it is because it is great to have. It scores highly on the KPIs. The other reason is the faster the peak speeds, the better the average performance,” Bennett said.
“From an engineering perspective, I'm keeping that base carrier free and pushing most customers up to 2.6GHz, where the capacity is."