I've not been on RCI but it's unusual for ships cabins to have kettles in them. You can order tea or coffee from room service any time you want. As for mobile phones, the answer is sometimes. Depends on whether or not you can pick up a signal. Most often than not i find that I can only use it in port or when I'm close to Port, although I did manage to use it for a few days in the middle of the Atlantic a few months ago which I found quite surprising.
I would refer to the RCI brochure on Voyager cabins to find the answer to your first question, though it is doubtful, as kettles in cabins are a very British thing ( stick to the likes of P&O if this is important to you). As to mobile phones, the only way that they will work away from land is via the ships satellite communications network. Most ships now allow you to use your mobile phone through this system, but it will be quite expensive! Once again just check with RCI for the specific ship that you are sailing on. Happy cruising.
I am south Africa with a south African passport I am married to a british citizen will this be a problem in taking a cruise will I need some sort of visa.
We have been on Voyager and kettles aren't supplied and travel kettles are not allowed. I don't know about phones but you can e-mail from the ship for a cost but the system is very slow.