The activation charge now seems to apply to all new customers taking out any Infinity package with the exception of Unlimited Infinity 2. http://www.productsandservices.bt.com/products/broadband/packages?Infinity=yes
I don't see any exceptions for this charge but you could try asking the Options team 0800.800.030 who may be able to answer it.
I suppose somebody has to pay towards the engineer to visit the cabinet or the exchange.
I was (though I had Sky normal broadband - not fibre).
Same here I wasn't charged for BT Infinity Unlimited 2 and I get connected tomorrow 🙂
I signed up for the Infinity 2 wasn't charged either.
The migration went pretty smooth apart from the issues I am having with an unstable Broadband but that is being looked into.
It's not to say that it wasn't unstable when I was with Sky - I just never noticed