There is a new app called Cadenza which is downloadable through Itunes, I'm not sure if its available on android also. This is a new brilliant concept which allows the student to play through some popular classical repertoire with an accompaniment. I tried it out myself. I think it's still in the development stage however as if the student is not yet comfortable with the piece - for instance if they stop playing - the accompaniment stops also and gets confused. The difference they were trying to get with this application compared with playing along to a CD, was that the accompaniment actually follows your tempo slightly like a real accompanist would. This is not perfected yet though, and I was a little frustrated with the responsiveness. Also, it wasn't loud enough without an additional speaker that needed to be attached to the phone. The idea however is good, and its a fun app to have a play with. I would still recommend playing along to a recording until its developed further in the meantime.
Here I write my musings on teaching, or other things that come up in lessons/relate to violin learning. Anything suggested is just that, suggestions and my thoughts and may differ from the opinions of my other music colleagues!