Why am I having trouble calling a mobile or landline?

To make a call, tap on the keypad button and dial the 10 digit number (US phone number) as you would with a regular handset. Once the 10 digit number appears, press the Call button.

Also, you can call a number from your Contacts in the Talkatone app. Tap the Contacts icon and scroll down to select the contact you want to dial. 

You'll see the Contact details of that contact. Tap the phone icon to the right of the contact's number to call them.

NOTE: In order to make international calls (outside USA) you have to purchase the International subscription or buy credits. You can find more information in the following link.