"Call not sent" when adding a call on Samsung Galaxy S6 Sometimes, when I am on a call and try to add a call, I get an error message that reads, "Call not sent". It only happens sometimes, and I can't figure out the pattern. It seems to be related to the number I'm calling, but not in any obvious way. For example this morning 917.533.9562 worked but 212.784.8053 did not.

I am on a T-Mobile Samsung Galaxy S6 (SM-G920T), Android version 5.1.1, and I use Google Voice for all of my dialing.

If anyone can me solve this I will greatly appreciate it. Thanks!
Unfortunately the update "broke" Google Voice on Note 4 and Galaxy phones (T-Mobile 5.1.1 update).

You can see information on this here:

We're all hoping that someone (Google, T-Mobile, Samsung) will care enough to fix it.