According to this BT press release, Openzone is coming to Starbucks in the UK.
No word on what happens to T-Mobile at Starbucks. I can't see why either need exclusive access to Starbucks - the Starbucks closest to me as I write this has already has both, thanks to BT's Wireless Westminster service. Alternatively, this could be a sign of T-Mobile more or less exiting the WiFi access point business in the UK. A quick check of their HotSpots in London had very few non Starbucks locations run by T-Mobile (they did list a lot of Openzone access points, as they have a roaming agreement with Openzone). And one of those T-Mobile HotSpots (at Waterloo Railway Station) appears to directly compete with an Openzone access point (I should go there and confirm).
Strangely, they haven't sent an email about this to Openzone customers - I stumbled across the news while looking for something else.