If you are not connected to a local network, you will not be able to make / receive a phone call. You will need to wait until you are in a location with network coverage / a stronger signal and then retest.
Failed phone calls are often the result of a phone number being dialed using the incorrect format. Please ensure that you are using the correct international dialing procedure as advised here:
Dialing Instructions For Outgoing Calls
Your call will now be routed through to the number you have dialed. When calling to a cell phone, your contact will need to ensure that their phone is switched on and connected to a local network to allow the call to complete.
If they have their phone switched off / they are outside of the coverage area, you may hear an automated recording stating that they are unavailable or alternatively, the call may go directly to voicemail. Please be advised that this will be considered by the network to be a connected call and therefore, the call would be chargeable.
If you are in a location where network coverage should be available but the issue persists, please refer to the “Failed Network Connection” articles that can be found on the Mobal support pages.