The Herald understands that Vodafone and 2degrees handsets were being picked up by Spark's trial network - a feature designed to accommodate 111 emergency calls being shared between providers - but then not being rejected for regular connections because of the configuration error.
Yesterday morning, Vodafone said it had sent a hit squad to Alexandra to investigate interference issues chronicled on a local Facebook page with "high priority".
Today, spokeswoman Nicky Preston said, "On behalf of our customers we're relieved that the root cause of interference issues in Alexandra has been identified as an issue with Spark's trial 5G wireless broadband configuration, and has now been resolved. Our engineers spent the past 36 hours working alongside Spark to investigate the matter."
She added, "We will continue to monitor the network closely to ensure strong service continues in the area for our customers."
The furore began when Geekzone, user "J" posted: "This is not a beat-up, our business [account] has been with Vodafone for approx 15 years, and apart from these issues lately I have no complaints.
"There have been several threads on Alexandra local FB pages about the frequent loss of connectivity.
"Phones receiving no signal and displaying a no-carrier message, Txt messages not being delivered till phones are restarted."
A spokeswoman for Spark said on Monday: "Our Spark 5G wireless broadband service in Alexandra is using 2600MHz spectrum, which is not a spectrum band that Vodafone uses in Alexandra. So it is very unlikely that any issues experienced by Vodafone customers are caused by the Spark 5G service."
Vodafone uses 700, 900, 1800 and 2100MHz spectrum in the area, Preston said.
2degrees also has two of its own cell sites in the area, at Alexandra and Clyde, and there is at least one of its customers being caught up in the problems.
"My wife's on 2degrees and multiple times it has lost all cellular connection until her phone has been rebooted," one Geekzoner posted.
Shades of XT stoush
The Alexandra interference incident immediately reminded one veteran Geekzoner of the company-formerly-known-as-Telecom's 3G launch in 2009.
In the run-up to the launch of Telecom's 3G network, branded "XT", Vodafone alleged interference with its network and sought an injunction in the High Court.
After an initial hearing, the pair settled out of court, with Telecom agreeing to install extra filtering gear at a cost of around $1000 per cell site.
The XT interference case occurred at a time when Spark was using 850MHz for its 3G service and Vodafone 900MHz.
One wrinkle next to 2009 is that Spark and Vodafone are using the same network technology partner in present-day Alexandra: Nokia Networks.
Spark turned to the Finnish company for its central Otago trial as it pursues a "multi-vendor" strategy in the face of the GCSB's ongoing ban against its 4G incumbent, Huawei. Nokia Networks is Vodafone NZ's longtime primary technology partner.
