A cross launch starts for the user in Teams but ends up opening a 3rd party client or application to make the call or use the functionality. Cross launches are inherently clunky and user-unfriendly but what you give up in ease of use you get back in Microsoft license savings. The question is whether the basic functionality and platform variances available from a cross launched integration are worth the effort – will business user deal with significant inconvenience to use Teams as a softphone.
Here are your choices:
Choice 1: You build a Teams Application with an embedded 3rd-party web portal. You can also include a chat bot in your Teams Application if you are relaying other PBX information into Teams Activities. Many of the largest competitors to Microsoft have taken this approach. When the user wants to make a call another client/app outside of Teams running on the same device takes over. TeamMate allows you to build a custom Teams Application per business to augment the Native MIcrosoft Teams dial pad.
Choice 2: You build a Teams Application with an embedded 3rd-party web portal and WebRTC. This approach is similar to Choice 1 with the addition of WebRTC to allow call setup from the embedded web pages in Teams. WebRTC is notably unreliable on mobile networks due to limits in the protocol.
Any integration you choose with Microsoft Teams means you will need to understand Microsoft user licensing and Microsoft enterprise credentials. TeamMate automates the Go Native options that use Direct Routing.