First, you will need at least two projects in the same organization (see Adding a new project).
You can configure which projects a phone is shared in from your Phones page. Click the phone you want to share, then click “Edit Settings”, then select the projects in the “Sharing” section:
When sending outgoing messages via a shared phone, the message will be copied into the project for the original phone (each message will appear in two different projects).
By default, all incoming messages will only appear in the original project where the phone was created, not any of the "shared" projects (even replies to messages sent from one of the "shared" projects).
To route incoming messages to the correct project, create a service with Custom Actions, add one or more conditions to match particular messages, then use the “Copy message to project” action.
For example, the actions below copy any messages starting with the word "arusha" to the project for a radio station in Arusha, while copying any messages starting with "moshi" to the project for a radio station in Moshi:
In addition to routing messages based on keywords (as in the example above), it's also possible to change the conditions to route messages depending on the contact's groups or custom variables.
However, Custom Actions can only refer to conditions and variables defined in the original project, not the other projects that you want to copy the messages to. This may make it difficult to route incoming messages correctly; in this case it may be easier to just have completely separate phones for each project.