Have you set-up Express talk with a VoIP service?
If yes, are you sure the service you signed up for allows calls to the number you are dialling? For example, if you don't have a paid account, it is unlikely the VoIP service will allow you to dial PSTN lines (i.e. regular phone numbers) for free thus resulting in "Declined."
If you are sure the service should allow calls to the number you are dialling, then it is also possible you are dialling the number incorrectly. For example, some VoIP services require you put in the area code (even for local numbers that normally don't require it), other services sometimes require the country code be prepended to all calls.