You can market your company on different websites and forums which help you to seek new clients for your company so that you will be able to get new clients.
Well i would suggest you that locate different companies number from net those you think can require call center support. Then try you do telemarketing first for fetching new clients. You can provide them all the statistics about your number of terminals and services that you can offer. I don't think giving an advertisement in newspaper will work.
Just ask your call centers to get new clients for company and they will get commission and then you will see the results.