Your topic is too generic because it does not specify which job title are you talking about, anyways i assume its for the title of Customer Support Representative or what is commenly known as CSR or agents. Apart from what my friend Eddie has mentioned i have some points to shared based on my observations and experience:
1-In the country where the industry is matured you get a job in a call center because it is one of the largest industries in the world.
2-In the country where its in introductry stage there are lots of job opportunities and potential for growth.
3-With were few months of work experience you get the knowledge in so many aspects like culture, history, behaviour of different people.
1-There are lots of jobs but no potential for growth in the company located in the mature market.
2-Cultural shock in case of off shore call center. Agent calling from a center located in India or Pakistan will have a longer learning curve in breaking through (making sales) because of the difference in the culture
3-Result in psychology problems like stress and anxiety.