Custom Social App Development

I'm seeking an experienced mobile app development team to create a production-grade social/messaging mobile application for both iOS and Android platforms. The app should include:

Core Features:
- User Accounts
- 1:1 & Group Chat
- Media Sharing
- Voice/Video Calls
- Notifications
- User Profiles
- Friend Connections
- Activity Feed
- Admin Panel

Requirements:
- Comprehensive development process with clear timelines and milestones
- High-quality design, robust backend, thorough QA, and smooth deployment
- Initial maintenance included

Ideal Skills and Experience:
- Proven expertise in building scalable mobile applications
- Strong knowledge of social networking and messaging features
- Experience with iOS and Android development
- Familiarity with backend technologies and cloud services
- Strong UI/UX design capabilities
- Solid QA processes and deployment experience

Please include in your proposal:
1. Proposed architecture & tech stack
2. Phased timeline with milestones
3. Cost breakdown (MVP → Phase 2)
4. Team composition and similar case studies
5. Post-launch support terms (SLA)

A short PRD can be provided upon request. Looking forward to your detailed proposal. Thank you!