Ok, I'm pretty frustrated now, spent the last 4 hours on this and even put out a lifeline to Chet... and yes I searched old threads... 
 
I just bought a Zumo 660 (came across too good of a deal to pass up from a friend so I did it)...
 
Anyways, when I pair my Scala and iphone to the Zumo I can hear everything just fine on the phone, problem is the person I'm talking to can't hear me? What am I doing wrong that the mic on the Scala is not working?? 
 
I had this same problem with my Nuvi 765T and ended up not pairing the phone to the GPS, down side of that is I don't get caller ID on the GPS nor can I access my phonebook with the GPS... I just assumed that this was a downside of a Nuvi but with the Zumo this is do-able... Am I wrong?? 
 
Please throw this dog a bone, pulling my hair out here... 

I run the 665 and Scala G4.
Well first off it is the Zumo 660/665 that is going to give you a problem. I had to go to http://www.zumoforums.com/ to search for alot of my problems with the bluetooth audio. To this day with updates and following the suggestions I still have problems with the bluetooth end of it.  For phone calls, if I'm stopped they can hear me but driving they seem to have a problem. I think it is more wind noise (Icon Alliance), because I can hear them.
BTW.....if  I remember correctly didn't you sell a 665 that you were givin? Did your pal pay you to take it? I know...
But I think between this forum and the Zumo forum you should be able to get it work.

 

I run the 665 and Scala G4.
Well first off it is the Zumo 660/665 that is going to give you a problem. I had to go to http://www.zumoforums.com/ to search for alot of my problems with the bluetooth audio. To this day with updates and following the suggestions I still have problems with the bluetooth end of it.  For phone calls, if I'm stopped they can hear me but driving they seem to have a problem. I think it is more wind noise (Icon Alliance), because I can hear them.
BTW.....if  I remember correctly didn't you sell a 665 that you were givin? Did your pal pay you to take it? I know...
But I think between this forum and the Zumo forum you should be able to get it work.

 

Good memory CP, actually it was a 665 that I had before and sold, it was a gift but I chose to use the $ on other farkles at the time... 
 
Is it possible that the reason they can hear you stopped is from the built-in mic on the Zumo? I actually did a test call (from the garage) and yes I could be heard, but once I walked about 5 feet away from the Zumo I could not? Which leads me to believe she was actually just hearing me from the Zumo mic... 

The Zumo has a built in mic?

Zg, I have a 660 smh10 and droid razr paired without an issue. I would recommend you upgrade the firmware to the latest version in the 660 and scala first off. I believe the major issue is usually getting the scala and iPhone on the right bluetooth channel on the 660. One I believe is full a2dp and the other is not so sometimes the phone can grab both channels and not allow the scala a channel to work on so the person might have heard you through your iPhone rather than the mic on the zumo.

One last thing I noticed with my 660 is its very tempermental when on battery power verse when the bike is running and from time to time will drop the Bluetooth while riding and I need to reboot. I tend to ride all the time with my droid paired directly to the sena playing pandora, no caller I'd but I can deal with it over the cumbersome feelng of everything going through the gps.

The Zumo has a built in mic?

Yes, for hands free phone when used in a car.
 

Zg, I have a 660 smh10 and droid razr paired without an issue. I would recommend you upgrade the firmware to the latest version in the 660 and scala first off. I believe the major issue is usually getting the scala and iPhone on the right bluetooth channel on the 660. One I believe is full a2dp and the other is not so sometimes the phone can grab both channels and not allow the scala a channel to work on so the person might have heard you through your iPhone rather than the mic on the zumo.

One last thing I noticed with my 660 is its very tempermental when on battery power verse when the bike is running and from time to time will drop the Bluetooth while riding and I need to reboot. I tend to ride all the time with my droid paired directly to the sena playing pandora, no caller I'd but I can deal with it over the cumbersome feelng of everything going through the gps.

Thanks D, I'll try the firmware update, good suggestion...

I have a Zumo 660, iphone and Sena SMH10B all paired without an issue.  Firmware and software upgrades on the Zumo and Scala is a great place to start.  let us know how you make out.  Thanks.

I think dion40 hit it on the head with the bluetooth channels. Maybe pair the G4 to the cell and try that, then to the GPS, that should narrow it down to the problem. I use the Zumo mainly for my MP3s, but have gotten tired of the Zumo dropping the connection after 40 mins or so. That plus it likes to go to mono more often than stereo. The only real solution for my limited patience span was to wire it to the G4...no problems, until I walk away from the bike.