For 36 hours, I have been trying out 4G in two cities where it has been launched by the EE network. Everywhere I've gone in London and Manchester, outside, indoors, on trains and in cars, I've used a speed testing application. And while I've seen some breathtakingly fast results, there has also been some worrying evidence that the speed and extent of the 4G network is being oversold.
Here is a selection of my results:
Monday 29 October, 14:55 GMT, Oxford Street: Download 53.74 Mbps, Upload 4.72 Mbps, Ping 33 ms
Picking up the 4G phone that I was borrowing from the EE store on Oxford Street, I gave it my first test - and it was very very fast. A 53Mbps download is better than the vast majority of UK broadband users could achieve at home right now - but obviously at EE's flagship central London store, the company had made sure the network delivered.
Oh dear - inside the BBC's new headquarters, things slowed right down. But then again, for some reason most mobile phone networks don't work at all inside the state-of-the-art building so this was better than many colleagues were getting.
Deep inside a chaotic Euston Station, more problems. The Speedtest app could not detect any data signal at all.
But once we took our seats on the Manchester train, 4G leaped back into life. The upload speeds looked startlingly good as we waited for the train to leave. As we headed out through North London, however, the 4G network seemed to disappear even before we had breached the North Circular Road.
Once we had arrived in Manchester, one of the 11 cities that were to go live with EE 4G on Tuesday morning, I was relieved to see that things were working.
At the cafe which kindly opened at the crack of dawn so that we could broadcast into BBC Breakfast and numerous radio stations, another pretty good result. That kind of speed might not look too startling - but if there is plenty of capacity it would make 4G a very attractive option to small businesses looking for an alternative to fixed broadband.
We headed north out of Manchester to see how far the 4G network stretched. As expected it melted away as we crossed the M60, but EE's 3G network proved surprisingly robust. This result from a village on the road to Rochdale looks excellent - but if you can get this on 3G why would you pay more for 4G?
Live from outside the BBC North base at Salford, we were back on 4G at a pretty respectable if unspectacular speed. Note the upload figure though - for anyone trying to send data rather than receive that will look very attractive. Mind you, inside the BBC building the 4G disappeared again. Vodafone has suggested that EE's brand of 4G won't be effective indoors - does that charge stick?
As our train headed out of Manchester, the 4G network seemed to stretch as far as Stockport. Taking advantage of some impressive upload speeds, I uploaded a video to YouTube in under a minute.
But there was a disappointing end to my 4G testing marathon. Arriving at my home in the remote wastelands of west London, I found that EE's network did not stretch this far. True - this 3G result is a lot better than my usual network gives me at home. But if 4G really is supposed to deliver a superfast future, indoors and outside, to 98% of the UK's population, wouldn't you expect it to work right across the nation's capital? Maybe the change of brand to EE is a tacit admission that the network just cannot deliver Everything Everywhere.