Sinch offers two options to service your existing numbers:
If you would like to use Sinch as your voice service provider (instead of your existing provider), then you need to port your numbers to Sinch. Porting your numbers will enable you to use both Sinch voice service and, if desired, text service for the ported numbers.
If you intend to keep your voice service with your existing provider, then you can host your numbers for messaging with Sinch. You can host your numbers if they are already text enabled or, if not, Sinch can enable text messaging so you can send and receive messages on your voice-enabled numbers (including landline numbers). Hosting your numbers allows you to use Sinch text services and leave your voice services with your existing voice service provider.