Pros
If you young, here is good chance to get experience but not for long time. Long time stay in CBOSS may work against you. Focus on getting knowledge about Telecom industry but don't think that way how CBOSS works is common especially interaction with customers.
Cons
Business is falling down, customers are leaving constantly, almost half of references at CBOSS site does't exist any more. At big events like Mobile Word Congress company can't present solutions just dancing girls and dinner with one of that girl (after MWC 2011 CBOSS been banned for at least year 2012). You will never get salary what was promised to you, huge bureaucracy doesn't motivate to reach business goals, just push you to follow formal rules. TOP Management replacement every one-two year makes absolutely unclear company strategy and goals and this includes promised bonuses.