Hello DH
O2 are using a company called "Be there" to provide their service, like most LLU providers they are putting equipment in areas which have high populations to ensure they get a good return. It costs a supplier nearly 30k per exchange the n they have to buy line in groups. So due to these costs unless there is great demand for their services (hence why they ask you to register to let you know when it is available) they just won't be available right away.
Hope this helps?
Michael.
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