Other issues under revue include termination fees and extra charges implemented for having a service fully restored after it has been restricted or suspended due to late payments.
"Consumers of communications services see headline prices fall," Ofcom chief executive Ed Richards commented.
"But they must not be misled. As they make their choice of provider, they need confidence that any additional charges are fair, transparent and justified."
The industry body will study whether such charges are transparent and whether the customer is made aware of them when they sign up to the service.
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