Hi, version 3.1 is supposed to help with disconnects. Please see this link:
However, Garmin released 3.4 which will include the changes in 3.1 and also makes the bluetooth compatible with more phones.
You need to go to www.garmin.com
and download their webupdater and run it with your Nuvi connected to the PC with a USB cable. It will check (via the Internet) if you need a firmware upgrade. The latest firmware version for a Nuvi 660 is v4.7. There is a second menu after the main firmware option that allows you to select additional software. Select yes and check the bluetooth 3.4 box and the Chipset "G" box if it's shown.. The Chipset "G" is the upgrade for the receiver in the flip-up antenna. Let it download. When finished, select to safely remove the Nuvi. You can now unplug the USB cable. Your Nuvi will reboot and load in the new changes. Whatever you do, don't turn your nuvi off! Let it go and update. You will see it say "Loader", then "Loading Software" and you'll see a task bar that says "Updating Bluetooth Software" and "Updating GPS Software" (if required). Once you get to the main menu and there are no more texts coming up on the screen. Press the power button and turn your unit off and then back on again. Check the GPS and Bluetooth firmware versions in your Nuvi. It should be 3.0 for the GPS and 3.4 for the Bluetooth. Check the firmware version if you selected v4.7. You will have to re-pair your phone with your Nuvi as the update erases any previous set-up. Let me know how it went for you. If you have trouble with this, let me know. I can do it for you. I have done it many times. Please rate my solution if you found it helpful.