Isn't Gig1 still available only with TV? If so, you may need a manned installation if you're a broadband-only customer although I don't see why a self-installation package comprising the hub 4, V6, cables and splitter shouldn't be sent out.
As for phone: it's new or house moved customers who get landline from the hub.
As Roger said your phone would stay the same as it is. Only new customers and moving customers are put on to docsis phones at the moment.
I don't have any experience with the SH4 myself, but only issue I've seen about Modem Mode is that you cannot run the SamKnows test while it is on. You would need to switch it back to normal to run the test before turning Modem Mode back on.