Its similar to the tethering watches, like the KW18. All the calls received by your phone will ring on your watch and depending on how the firmware is set up, may include contact information of the caller, if they are in your address book. You have the option of either answering the call on your watch or using your phone to answer the call. You should also be able to initiate calls on your watch using your phone for the connection. Generally you will select either BT or Local (Sim card), if you have one installed, to make the call. This is how it works on the tethering watches like the KW18 I mentioned.
For those not familiar with tethering watches and need to kill some time before the new firmware is available I suggest you watch this video by Mr. Ticks. You will need to start it back at the beginning.
joint000. It would be just like with your phone on speakerphone. If you want a private call on your watch you would have to use a BT earbud or other private listening device connected to your watch. But just like your phone they could still hear your side of the conversation depending on how loud you talk. Some people think they have to shout into their phones.