Building a Local SMS Sync Agent: Bridging Samsung Messages to macOS Without Twilio

```html

This post documents the engineering decisions and implementation details behind building a standalone SMS synchronization tool that aggregates messages from multiple sources—including a Samsung device—without relying on external SMS gateways like Twilio.

Problem Statement

The existing SMS infrastructure in our codebase relied on Twilio credentials for message retrieval and sending. However, we needed to:

Read historical SMS from a Samsung device without Twilio API calls
Aggregate SMS across multiple phone numbers and sources
Run as a background daemon on macOS using launchd
Export conversations in a queryable format for digest generation
Minimize external service dependencies

The existing SMS export at /Users/cb/Library/Mobile\ Documents/com\~apple\~CloudDocs/Documents/jada_sms_export.txt provided conversation history but lacked real-time sync capability and automation.

Technical Architecture

File Structure & Components

We created two primary artifacts:

/Users/cb/Documents/repos/tools/samsung_sms_sync.py — The main synchronization engine
/Users/cb/Library/LaunchAgents/com.cb.samsung-sms-sync.plist — The launchd daemon configuration

The Python script handles:

Reading the static SMS export file as the source of truth
Parsing conversation threads with phone numbers and timestamps
Filtering messages by date range (e.g., April 25-29)
Extracting specific conversation threads (e.g., +15302623442, Sergio's number)
Generating structured digest emails via AWS SES

Integration Points with Existing Infrastructure

Rather than building a full Android bridge, we leveraged existing resources:

SMS Export File: Static file containing historical Samsung messages previously exported and stored in iCloud Drive
Twilio Credentials: Located in .secrets/repos.env (referenced but not required for this implementation)
AWS SES: Used for sending digest emails via existing voice agent infrastructure
Voice Agent SMS Handlers: phone_agent.py contains SMS capability logic we could reference

Implementation Details

SMS Export Parsing

The export file uses a structured format with conversation headers and message entries:

Phone: +15302623442
Name: Hostess Name
---
[timestamp] Your text here
[timestamp] Their response
---

Phone: +16194164690
Name: Another Contact
---
[timestamp] Message content

Our parser extracts these sections using regex and structured line parsing, handling:

Multi-line message bodies
Variable timestamp formats
Contact name inconsistencies
Chronological ordering within threads

Conversation Filtering & Digesting

We implemented hierarchical filtering:

Date Range Filter: Extract messages within April 25-29 window (parameterized)
Contact-Specific Filter: Isolate Sergio's full thread for deep analysis
Context Preservation: Include conversation headers (phone, name, last activity)
Digest Generation: Summarize key themes, action items, and financial data

The digest email identifies:

High-priority items requiring immediate response
Financial transactions and amounts
Equipment/operational issues
Schedule-critical events
Contact-specific action items

Daemon Configuration

The launchd plist at /Users/cb/Library/LaunchAgents/com.cb.samsung-sms-sync.plist defines:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" 
  "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.cb.samsung-sms-sync</string>
  <key>ProgramArguments</key>
  <array>
    <string>/usr/bin/python3</string>
    <string>/Users/cb/Documents/repos/tools/samsung_sms_sync.py</string>
  </array>
  <key>StartInterval</key>
  <integer>3600</integer>
  <key>StandardErrorPath</key>
  <string>/var/log/samsung-sms-sync.err</string>
  <key>StandardOutPath</key>
  <string>/var/log/samsung-sms-sync.out</string>
</dict>
</plist>

Key design decisions:

StartInterval: 3600 — Runs hourly; can be reduced for more frequent sync
Log files: Standard output/error to /var/log/ for operational visibility
No RunAtLoad: Launches on schedule, not at boot, reducing startup load

AWS SES Integration

Email delivery uses the existing SES client from the voice agent infrastructure:

Sender: Configured identity verified in AWS SES console
Recipients: Default to c.b.ladd@gmail.com (configurable)
HTML Body: Formatted digest with headers, bullet points, and structured data
Plain Text Fallback: Readable plaintext version for compatibility

The script constructs email via boto3 client:

client.send_email(
    Source='noreply@sailjada.com',
    Destination={'ToAddresses': ['c.b.ladd@gmail.com']},
    Message={
        'Subject': {'Data': 'SMS Digest: April 25-29'},
        'Body': {'Html': {'Data': html_body}, 'Text': {'Data': text_body}}
    }
)

Key Engineering Decisions

Why Not Use Twilio for This?

Twilio would add API call overhead, rate