Skype and mobile broadband

I bought T-Mobile pay as you go mobile internet with USB stick 120 http://support.t-mobile.co.uk/help-and-support/index... which is ZTE MF626 http://www.zte.com.au/main/MF626.htm. This stick supports 3.6Mbps. I'm within very good T-Mobile range, my conection is HSDPA. The internet is really fast but skype connections are very very poor. Why?

It all depends on the connection speed of the person you are talking to. I can get 4 to 5 mbps on HSPA+, but the person I speak to in the Caribbean Struggles to get 1 mbps. So we can only use voice calls.

VOIP technologies require fast connections i.e. low latency. So even if you have a connection with a high download \ upload capacity you won't necessarily have low latency and therefore your Skype conversation will be poor. Try Vodafone for low latency in the UK

Skype recommend that the download \ upload speed is 500kbps for a video call

Best 3G data coverage
I can not say Three has the best coverage its the worst network of them coverage wise (Three network map is an Lie if you want there real coverage map use 3g T-Mobile map as most of the Three network is based on an 50/50 share with t-mobile)

more likely T-mobile and Orange now with native home network now coverage wise (it use t-mobile or orange witch ever is the better signal now most of my T-mobile phones use Orange network and i tend to agree when i looked at T-mobile coverage map compared to Orange on there own site)

but i agree good phones, good price plans, best data packages (as long as your not indoors)

but t-Mobile now offer unlimited download with the full Monty offer (mite need to use an VPN to bypass the Traffic shapers thought on t-mobile to get full speed if you need it thought)

and advertising is not allowed (the web site in question that you posted mite not be allowed as what it leads to)

I have faced this problem often with the skype. It supports VOIP technology, so this problem does not present for longer time.
Have patience, it will be Ok.