Automatic diallers can result in a silent call if more phones are answered than there are agents to handle them. To help remove the chance of a silent call, Ofcom has, until now, insisted that recorded messages have to be played within two seconds of the phone being picked up.
But this has now been amended so that the two seconds can begin after the person answering the phone starts speaking.
The move, which follows the Government's proposal last month to increase the fines on companies that flout silent call rules from £50,000 to a maximum of £2m, is in response to business concerns about the two-second rule's effects on outbound telemarketing.
In July the Confederation of British Industry issued a document arguing that the two-second rule would have a negative effect on business, as two seconds does not allow answering machine detection technology "sufficient time to operate".
Ofcom has amended the rule to "make it easier for diallers to detect when a call is being answered by a real person or an answering machine," Ofcom says in a statement on its website.
The change is bound to be controversial with consumer groups that have campaigned for silent calls to be banned entirely.