Only EE (formerly called Everything Everywhere) will be able to offer islands of 4G connectivity to the 4G-capable iPhone 5 when it arrives in the UK.
The Apple smartphone will be available from every network operator, but two - O2 and Vodafone - will never be able to give the phone the fastest possible mobile broadband.
Apple's latest iDevice comes in three flavours: one supporting CDMA and two GSM versions that differ by the LTE bands they support.
The UK model (A1429) supports LTE in three different frequencies, but just one of those is likely to carry 4G signals in the foreseeable future, and only for two of the UK's operators - EE and Three. This leaves everyone else with 3G connectivity at best.
There are 42 officially recognised bands for LTE, but rollouts are coalescing around the more-popular bands by region, based on what history has made available. In Europe that means 2.6GHz (the 3G-expansion band) and 800MHz (cleared of analogue TV), with 1800MHz popping up in some places including the UK.
In America, TV cleared out of the 700MHz band, and never filled the 2.1GHz (3G) band, while in Asia the 850MHz was left largely empty, so what we have is two models of GSM iPhone aimed at the US and Asia, with Europe picking up some dredges from the middle.
The version of the iPhone 5 on UK shelves will support LTE at 1800MHz, ideal for EE which owns the whole band, and for Three, which is in the process of acquiring a chunk, but not so good for Vodafone and Telefonica (aka O2) as they are unlikely to ever get one.
The iPhone can also use LTE at 850MHz, but via a frequency pairing that fits well in Asia but does not map to the spectrum being auctioned off next year in UK's 4G auction. So this will never be usable in Blighty.
The third supported LTE band is 2.1GHz, in which all the UK operators have a stake, but that's full of 3G and unlikely to get cleared any time soon.
Half a dozen countries in Europe have already deployed LTE in the 2.6GHz band - where no iPhone dares to tread, so operators in Denmark, Norway, Switzerland and elsewhere will have to explain to their customers why the LTE iPhone won't work on their LTE networks.
None of this is Apple's fault: rival phone makers face the same problem and are coming up with similar answers.
The problem stems from the market-driven approach to specifications (as opposed to the mandated frequencies of 3G, which ensured international compatibility), and the flexibility of the LTE standard, which happily works across the radio spectrum in slots of varying sizes.
This is an admirable flexibility in a standard, but a nightmare for those trying to make kit which "just works". ®