Kevin:

So, you are going to go for the Kenwood THF6A?  I know you will love it!

Anyway, as for speaker mics, I don't think the Radio Shack one will work.  I
had the same problem when I got my THF6A, and had to get another mic.  My
understanding is that the leads on the mic plug are the reverse of  the
Radio Shack leads.  First, I tried an MFJ speaker mic, and was not at all
satisfied with the quality and the modulation.  So, with the advice of
several folks on the list, I purchased the Kenwood SMC33 model, and like it
a lot.  There are other Kenwood mics you can buy, but this one really does
seem to work the best.  It costs about $65, if I remember correctly, but is
really worth the money.

Let me know what you end up doing and if this helps.

Again, I know you will love the THF6A.  There hasn't been a problem with it
yet that I haven't been able to solve, especially with the help of folks on
this list.  One small drawback to keep in mind, though, is that the THF6A
gives you no audible indication when the battery pack dies;  once it dies,
it really dies!

But, that's only one small problem I have found.

Vy best 73 from Tom Behler:  KB8TYJ