Oh dear... (my chat with T-Mobile customer services - they pro-actively initiated the chat, I wasn't looking to speak to anyone):
Thank you for choosing T-Mobile. A T-Mobile Sales Adviser will be with you shortly.
You are now connected with Daniel.
Daniel: Hi there, my name is Daniel. I am part of the dedicated T-Mobile Online Sales Team. How can I help you with your new order?
Mike: Hi Daniel, I'm looking to arrange a PAYG plan for an iPhone 4.
Mike: Do you know if T-Mobile retail stores will be stocking the iPhone 4 on June 24th or if there will be a T-Mobile pre-order for the phones? (Easiest thing for me would be to purchase one and activate it in the shop on the day).
Daniel: For that you need to register yourself on the website .
Mike: I also had another question about network coverage - I've read in the press that Orange and T-Mobile have merged and will be sharing masts at some point - has this happened to your knowledge? I was with T-Mobile for several years as a business customer previously and whilst the customer experience was good, the network wasn't great in the country.
Mike: I've done that (registered on your website)
Daniel: And T-mobile will let you know when the phone comes.
Mike: I'm currently with O2, do you know if it is possible to port an O2 PAYG number to T-Mobile?
Daniel: Yes definitely it possible.
Mike: Thank you (my O2 number was originally a T-Mobile contract number!)
Mike: Ok, regarding your network - do you share masts with Orange at all?
Mike: Or do you know when this might happen?
Daniel: Not yet.
Daniel: for that you need call customer service department.
Mike: Ok, thanks.
Mike: I want two of these, I'm leaning towards Orange for the network (hence my mast sharing question) and T-Mobile for the tariff and the international boosters. I've already signed up with the T-Mobile website for notifications but haven't received anything.
Mike: Apple's already been taking pre-orders today.
Mike: Is there anything you can tell me about possible availability?
Daniel: Please call customer service the number is 150 or 1818.
Daniel: they will be able to help you?
Mike: That would take me to O2 customer services 
Thank you for chatting with us.
^ Then he cut me off!