Contact names searching in huge database

I have a project where the main task is to search for contact names stored in database. For example, I have web application where I type in searching field some cell number: "777555444" and as result it returns me a proper name: "John Doe". If proper name was not found, cell number is appended to another database table of unknown numbers.

The database could have a billion of contacts. So: 1) the searching should be performed in multithread fasion 2) the maximum memory saving by database (loading into RAM and loading memory from the disk in case of insufficiency) 3) regular database indexation in case of searching for proper "contact names - cell numbers" that where not found before. For example, admin uploaded some list of contacts to the database. But user have already performed searching for one of cell number existed in that uploaded list. It means that cell number is in the table with unknown numbers and now it should be deleted from there.

So, what is the best way to implement all this specific features? What techology should I use? For example, my preferable choice is python/Django/mysql. But is that usable in my case?

Off course, I just ask you for a global approach in my questions.

Thanks in advance.