There may be some restrictions when using different phone numbers. Numbers are best used for local, two-way voice communication and for sending and receiving SMS from local mobiles rather than internationally.
A number capability can be either SMS, MMS or Voice. You can filter the capability type in the Phone Numbers section in the Enfonica Console when purchasing a number.
If a number only has a voice capability, you will not be able to send an SMS with it. Be sure to choose a number with the right capability for your project. You can check phone number capability once you select the number in your inventory.