Is getting an iPhone 4s now a waste?

I currently have a blackberry and pay £20 a month. The main reason for changing my phone to iPhone is so that I can iMessage and FaceTime with a front camera as my sister has moved to New York.

I realize that there have been been a few new upgrades since the 4s but will it be a waste of my money (it's still £20 a month for 2 years) if I get one? I.e. Will I be able to FaceTime etc or will they bring out some new thing that means I can't download apps etc.

Any help would be really appreciated

Well, you will still be able to FaceTime if you were to get an iPhone4S. Apple has a feature for every Apple device called "iMessage" it allows you to text and video call anyone as long as you have an internet connection and each person has an Apple device. Since the iPhone4S has both a front facing and back camera, you would be able to FaceTime.
Apple has also recently let each iPhone's internal technology update as each update is made. Which means your iPhone4S can have the internal technology as the iPhone6's, unless they make like a retina scanning feature for the camera.
Do more research with the iPhone6's new upgrades to see if it's worth it.
Note: the iPhone4S has the old charger while the iPhone5, and probably iPhone6, will have the new charger. It doesn't change the phone, but it might matter to you. So. Yeah. Hope this helped!

It would smarter to wait until the iPhone 6 comes out this autumn, then decide. The iPhone 4S could be very cheap if it is discontinued. I'm not an Apple fan but I think it would be wise to save up until the release date of the "6".

I would say yes because I would be three 3 versions older when IPhone 6 will be released in September.

Not necessarily a waste since it would still get updates at least through iOS 9 (last iOS 8 specifically) & yes you could still FaceTime of course. So at least for a year it would be actively supported.