Build SIP Auto-Dialer Utility

I need a self-contained application that reads up to 20,000 phone numbers from a plain .txt file (one number per line), logs in to our SIP trunk with the credentials I will supply, and starts calling. The tool must be able to place up to 4 simultaneous calls and negotiate any of these codecs: G729, G711A, or G711U.

While it is running the interface should always show:
• the most recently dialed number
• how many numbers remain in the list

A pair of clearly labelled Pause and Resume buttons must stop all active calls instantly and restart them on demand without closing the program.

For each attempt the program writes a simple text line to an output file noting the number and whether it was ANSWERED or NOT ANSWERED. Dialing can be sequential or in batches of four, whichever is faster while respecting the 4-call limit.

Deliverables
• Executable application plus full source code
• README with setup instructions and any dependencies
• Sample input and output text files to confirm format

Acceptance criteria
1. Successfully places up to four concurrent calls through our SIP trunk using the specified codecs.
2. Processes a 20,000-number text file in a single run without crashing or memory leaks.
3. Generates an output text file with accurate status for every number.
4. Pause/Resume buttons work instantly and the on-screen counters update in real time.

Language, platform, and SIP libraries (e.g., PJSIP, Asterisk AMI, JAIN SIP) are up to you as long as they meet the above requirements and compile cleanly on a current Windows or Linux desktop environment.