These are the new WnW conditions:
WnW = 1GB limit, web browsing from handset, email from handset - nothing else. £7.50/m.
WnW Plus = 3GB limit, web browsing from handset, email from handset, use handset as modem, stream media, download files, use IM. £12.50/m
WnW Max = 10GB limit, web browsing from handset, email from handset, use handset as modem, stream media, download files, use IM, use VOIP. £22.50/m
Looks like the new £7.50 WnW is a lot more restrictive than the previous package. You could download files on the old one as long as it wasn't streaming. With these new packages, downloading is only allowed on the WnW Plus and Max.
Kind of kicking myself that I didn't phone up T-Mobile a week ago and asked to be upgraded to the old WnW Pro for £10 a month. This allowed modem use and streaming data.