If your employer is a well known company, and details of it can be easily found over internet, then it is unlikely that they will call. First thing they verify is that your employer in genuine or not. If yes, they may accept the statements in your experience letter as it is. Only if they have doubts like they cannot find your company details over internet, or your job role does not match the business profile of your company, or the kind of roles does not align with your education or years of experience, then they might give a call to cross check if your letter is genuine or not.