Second Line App for Private Secondary Phone Numbers
Jagwinder Singh
Project Overview
I built Second Line from scratch to provide users with a private, secondary phone number for calls and texts without requiring an extra SIM card. The app aims to solve privacy concerns, facilitate business communication, and simplify international calling for users on a single device.
Problem Statement
Many users need multiple phone numbers for work, personal life, or online verification. Current solutions are either:
Expensive (buying extra SIMs or plans)
Inconvenient (switching devices)
Limited (in features, coverage, or reliability)
Second Line was designed to bridge this gap, giving users seamless access to a virtual phone number that feels as reliable as their primary line.
My Role & Responsibilities
As the sole developer, I managed end-to-end development, including:
Architecture & Backend:
VoIP integration using WebRTC/SIP for calls and SMS.
Number provisioning via telecom partners.
Push notifications for inbound calls & messages.
Frontend & UX:
Designed intuitive UI/UX using SwiftUI.
Implemented features like call history, inbox, and number management.
Payments & Subscriptions:
Integrated Stripe & Apple In-App Purchases for subscription plans and credit-based features.
Security & Privacy:
Encrypted user data and communication sessions.
Implemented account recovery and secure session persistence.
Testing & Reliability:
Automated testing for VoIP flows and network edge cases.
Crash reporting & analytics with Firebase.
Key Features
Acquire a secondary phone number (US, Canada, Finland, others).
Make/receive calls and send texts without exposing your primary number.
International calling & SMS support.
Subscription-based premium features (unlimited calls & texts).
Privacy-first architecture: no data leaks, secure cloud storage.
Technical Challenges & Solutions
VoIP Stability:
Challenge: Dropped calls and message delivery issues over weak networks.
Solution: Implemented network fallback logic and real-time retransmission for messages.
Number Provisioning:
Challenge: Automatically assigning valid, local numbers in multiple countries.
Solution: Integrated SIP trunking with telecom providers and cloud-based number management.
Payment & Subscription Transparency:
Challenge: Avoid confusing users with credits vs subscription limits.
Solution: Built clear UI, in-app receipts, and detailed FAQs for billing.
Security & Account Recovery:
Challenge: Users switching devices without losing data.
Solution: Implemented cloud-backed encrypted session storage and secure recovery flows.
Key Learnings
VoIP reliability and message delivery are critical for user trust.
Clear subscription structures prevent confusion and support retention.
End-to-end control over the stack (frontend, backend, and infrastructure) allows faster iteration and optimization.
Impact
Successfully launched on the App Store with [insert number] downloads in [insert timeframe].
Reduced user complaints by X% through proactive error handling and recovery flows.
Users now manage multiple phone lines efficiently on a single device with improved privacy.
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Posted Mar 3, 2026
Developed Second Line: Get a private 2nd phone number for calls & texts, keep your real number private, and manage multiple lines on one device
