You can normally try several free IQ tests on websites like www.Iqtest.com The most reliable of websites would be some that have tests based on the MENSA criteria. Since, customer service jobs are normally oriented towards the UK, Canadian, American and Australian markets you could try their respective language proficiency tests as well and practice comprehension. There is no homogenized test format for call centers. They normally articulate and design their tests according to their job requirements and training assessment.