Since nobody else has posted a recommendation for a "trainer" radio, I'll throw one out there:

http://www.hobbypeople.net/prdcls/r463938.asp

Hobby People has the Airtronics VG400 radio system on sale for $99.99 with transmitter, 7 channel dual conversion receiver, tx and rx batteries, wall charger, power switch and 4 Airtronics 94102Z standard servos. This radio will also work as a buddy box on Airtronics higher end radios, including the 2.4Ghz FHSS RDS8000, if you choose to upgrade later.

I believe a simple radio is a good thing when training. The student needs to focus on flying essentials and doesn't need unnecessary distractions. I still fly with my Futaba 4YBF even though I have a 7C now. The 4YBF is great for sport planes, can be used as a buddy box, and comes in handy for using with various flight sims.

If there's a down side to have a good spare 4-channel sport radio handy, I sure can't think what it might be.