There are some other Salesforce apps that will also allow you to use the Mercury SMS integration.
If the Salesforce app is on the SFDX platform, you should be able to use Mercury SMS through this app. Examples of this are:
However, if the Salesforce app uses a different platform, it's unlikely to work natively with Mercury SMS.
Examples of this are:
If you're unsure, please ask us and we'll let you know.