Fetches a list of available bills for the active number.
This tool does NOT download the actual bill PDFs, it only lists their metadata.
Use the `download_bill` tool to get the file content.

Fetches a specific bill or its itemized record (EGN) and returns it as a PDF image/document.
The binary PDF content is wrapped in an Image object for proper serialization.
- bill_number: The number of the bill to download, found via `list_bills`.
- document_type: 'bill' for the main invoice, 'egn' for the itemized record.

Switches the server's active context to another phone number in the account group.
Use `get_phone_numbers` to find the `subscriber_id` for other numbers.

Enables or disables a specific SIM setting for the active number.
Use `get_sim_settings` to see available setting keys (e.g., 'roaming_barred', 'data_barred').
This is a low-level tool. For roaming, it's easier to use the `toggle_roaming` tool.

Updates a specific call forwarding rule.
- condition: The condition to change. 'alle' (all calls), 'nann' (no answer), 'wtel' (when busy), 'nerr' (not reachable).
- target: The forwarding target. 'd' (deactivated), 'b' (voicemail/box), 'a' (another number).
- target_number: The phone number to forward to (required if target is 'a'). Must be in international format, e.g., +43...
- delay_seconds: The delay for 'nann' (no answer) condition.

A simplified tool to enable or disable international roaming.
This is a high-level action that modifies the 'roaming_barred' SIM setting.