Then there were 3: Another UK mobile network borged ...

Analysis Telefonica has sold O2 to Three big-daddy Hutchison Whampoa for £10bn - and it pretty much had to. Here's why.

Telefonica had shown its hand in trying to flog its O2 biz to BT, revealing that it wasn’t interested keeping the brand; Telefonica smacks of never really having its heart in the venture.

With BT buying EE, and Hutchison Wampoa - the owner of Three - buying O2, there are lots of things which need to be considered.

The most obvious is this: what does going from five networks (when Orange and T-Mobile were separate) to three mean for mobile network competition in the UK?

A key ingredient here is radio spectrum. When EE merged Blighty's T-Mobile with Orange, Ofcom forced EE to flog off some of its 1800MHz holdings. The question is, if these latest mergers go ahead will another round of re-balancing be necessary. Let’s start by looking at who has what today.

The table below shows how many MHz each operator has at each frequency band - more MHz means more bandwidth, so more people can be supported by each cell tower or subscribers can get faster mobile data access.

We'll get some of the less obvious stuff out of the way first or else it will niggle.

UK Broadband (UKBB) is the service sold under the name Relish, which uses 4G to provide mobile broadband. The odd 6.6MHz of 1800MHz spectrum, owned by BT, is the DECT guard band. It’s planning on using this for the Onephone service.

Talk Talk also owns a DECT guard band licence for that frequency range – in fact, there are twelve licensees which all have rights to the same spectrum and have to play nice. TalkTalk wants to get Ofcom to allow it to use that guard band for LTE. However, the regulator's response when we asked them about that was: “It’s up to the other licensees.”

Getting eleven rival companies (BT counts as two) to agree on anything will be just like herding cats.

The 2600MHz is listed as paired and unpaired, and is used by different technologies. The paired frequencies use frequency division duplex (FDD) and unpaired is used for time division duplex (TDD) communications. The vast majority of equipment uses FDD but it’s shifting to TDD, which is better for balancing large numbers of users in a cell area.

While some spectrum allocations are more equal than others - lower frequencies have more range and so need fewer cell sites to build coverage, for example - it is in the national interest to share the frequencies fairly or at least in a way that doesn't destroy competition.