The 676 and 680 are essentially the same unit with a different key layout. I think (and I could be very wrong, yet again...) that the 880 has similar internal hardware, but includes a color screen (with 8 buttons instead of the 4 on the others!), even more same shaped buttons pressed together reminiscent of Ford factory radios in the early 90s, and a charging base station.

Now that's a run on sentence.

I am the Doctor, and THIS... is my SPOON!