When you create a free Dynamics Customer Service trial, you will get sixty minutes of PSTN Calls (US Toll-free Numbers).
After 60 minutes, you can bring your SIP-Trunk via Azure Communication Services or buy a dialing plan via Microsoft. If you are in Europe, you must go with the SIP-Trunk integration. This is a straightforward and menu-based setup. Your SIP-Trunk provider should give you an FQDN of "your" Session Border Controller and a Port. Even though direct routing in Azure Communication Services is still in preview, Microsoft fully supports it on a GA level if you use it with Dynamics 365 Customer Service Enterprise.
First, go to your OmniChannel Admin Center.In the site map, select Phone numbers in General settings.
Leave the Omnichannel Admin Center window open, open another tab for the Azure Portal, and configure the SBC/Port for Direct Routing.
Go back to your Omnichannel Admin Center tab and configure your phone numbers.
The new phone number will be displayed in the Phone numbers list and is ready for setup. You can now connect it to a voice workstream, configure outbound calling, or even assign it to an agent.
SMS is not supported with direct routing
if you are deploying for production, you should go for a carrier with post-paid contracts and a managed SBC Solution on the carrier site. Here you will get an FQDN and Port of the Carrier side, and you are done.
For example, I will describe how to configure a development direct routing connection via TELNYX.
You are now required to assign a Number to the Azure Communications Resource connection you created.
Create an Outbound Voice Profile and assign it to the connection you created above.
Configure some workstreams with the newly created numbers and test inbound and outbound calls.
Also published here.