W'n'W standard does not have HSDPA enabled, you need W'n'W Plus.Before Oct YB it did but this has been removed and unless you are very lucky (some people have been) they will not enable it for you and you will need plus which is 5 GBP/ month more but has a FUP of 3gig rather than 1 and you can use your phone as a modem.
348 is std 3G HSDPA is up to 1.8 - usually get 7-800. 3t is being increased to 7.2 but very few phones can use more than 1.8
If he's getting the H he's either one of the lucky ones or T-Mo is throttling his data rate on a server.
I got HDSPA on a 100MB-limited 20p calling bundle from eXpansys. Before the third tech saw HSDPA on my account and figured out enable>activate>'push it through', the first tech told me I had to pay another 12.50 for Web 'n' Walk Plus. This actually agrees with your £5, because the total is £27.50 just like Flext 20 + Web 'n' Walk + £5.
In my case, this was a training problem at T-Mo. CS had been adamant about "No HSDPA without Web 'n' Walk Plus". Two techs looked at the 'HSDPA' on my account and didn't know why it didn't work when it had been 'enabled'. The third tech had seen such a problem before and looked on another screen to see that it hadn't been 'activated'.
Again, since antlane's getting the H, I'd first try other locations.
antlane: if you are in the City, go out to Canary Wharf. I get between 500 and 1000 Kbps on dslreports speed test there when the H is showing.
If that doesn't help, tell CS you have a tech detail question. Don't mention HSDPA to CS. They won't help. Get a tech to 'enable' AND 'activate' HSDPA if they can see it on your account.
"They who have put out the people's eyes reproach them of their blindness." -- John Milton