Can I use the 3G Gear S2 (AT&T) without activating a plan on it?

The watch can be used standalone which means it's a data plan. 5.00 I pay for on Erizon. I had a Bluetooth eabled only prior. Like it does more.
 
I currently have a non-mobile share plan with AT&T, and I do not want to change up my plans. Could I just purchase the 3g device ($299.99) and simply pair it up with my phone?

The reason I want to do this is to take advantage of the speaker on the Gear S2. It is practically the same price as the non-3g, so I'd rather buy the version with the speaker.

Would the speakerphone work via Bluetooth with no AT&T plan?

I'm not too interested about just bringing my watch while my phone is at home, I only care if the speaker works.

Also, without a plan on the watch, could the 3g/4g band be turned off somehow to increase battery life?

What are your guy's experience and thoughts with the 3g device?

I have one you really can not hear the caller that well. And it likes to make calls when you bump it