Cross-Platform Messaging App Development

I am looking to develop a comprehensive messaging application that encompasses not just text messaging, but also voice and video calls, with the added functionality of being able to attach files from Gmail.

Key Features:
- Messaging: The app should facilitate seamless text communication between users.
- Voice and Video Calls: Incorporating high-quality voice and video calling features is a must.
- File Sharing: Users should be able to share files, with a particular emphasis on being able to attach files from Gmail.

Platform Compatibility: The app needs to be developed for both iOS and Android platforms.

User Authentication: The app should feature a social media login for user authentication. This will not only streamline the login process but also enhance the app's reach and usability.

Ideal Skills and Experience:
- Proficient in cross-platform mobile app development, particularly with iOS and Android.
- Experienced in developing messaging applications with voice and video call functionalities.
- Familiar with integrating social media logins for user authentication.
- Knowledgeable in implementing file sharing features within an app.

Please provide a portfolio of similar projects you've worked on, along with your estimated timeline and budget.