NBR graphic by Paul Slater.

On internet forums, and a torrent of comments following NBR's original article on Vodafone and Telecom's mobile network inteference case - about to hit the High Court - there has been a lot of discussion about whether an 850MHz and a 900MHz mobile network can in fact happily exist.

In fact, a real-life example lies just across the ditch.

Swedish telco infrastructure maker Ericsson points out that in Australia, Vodafone's 3G network, operating in the 900MHz band has had no issues coexisting with the 850MHz 3G network operated by Telstra.

True, any communication about eliminating interference would have been eased by the fact the same company - Ericsson - is the builder of both networks. But it underlines the fact that it can be done.

Kursten Leins, Strategic Marketing Manager, Ericsson Australia says, "Telstra's W-CDMA 850 network (NextG) has been operating alongside GSM networks for the past two and a half years and more recently with W-CDMA 900 networks in Australia. Networks can operate in both 900MHz and 850MHz so long as the necessary filters are in place to avoid interference where the two bands overlap or meet."

Despite its bull run in Australia, where it’s been involved in all carriers’ 3G builds, Ericsson has been shut out of recent action here.

Telecom (NZX: TEL) is partnering with Alcatel-Lucent to build its 3G network; Vodafone NZ with Nokia-Siemens, and NZ Communications with China’s Huwawei.

Vodafone says the situation across the Tasman proves its case.

If Telstra shelled out for filters for its 850MHz W-CDMA network, then Telecom should do the same here.

Telecom chief executive Paul Reynolds counters that he has - without admitting any interference - offered to work with Vodafone on installing filters.

However, the two companies have been unable to agree on who should pay for the filters - an issue which seems central to tomorrow's High Court hearing.