Big Data vs Relational Database on making structure of Data-ware house for telecom data analysis
Rule of Thumb: Does your workload fit with "traditional" approaches? Like oracle? Oracle can handle "00's of thousand of data of call" so does other databases like MySQL and SQL Server. You start looking into "Big Data Tools" when these solutions start to break. It's a pretty old video but it has some good insights: http://www.youtube.com/watch?feature=player_embedded&amp;v=5keh0UU0mNo 

Also I like the answer by Jeff Hammerbacher asnwer to similar question. Start at 27:01 http://www.youtube.com/watch?v=SVxc9lhMA0M

You could also consider reading the book "Planning for Big data" (free)
http://parasdoshi.com/2012/05/18/want-to-learn-about-bigdata-read-oreillys-book-planning-for-bigdata/