mobile app that includes a call option

I am looking for a mobile app developer who can create a mobile app for both iOS and Android platforms. The main functionality of the app should include a voice call option. The client has no preference regarding the existing designs or the need for creation.

Ideal skills and experience for the job:
- Proficiency in app development for both iOS and Android platforms
- Experience in implementing voice call functionality in mobile apps
- Ability to work with existing designs or create new ones based on the client's preference