The mobile phone retailer questioned three BT newspaper adverts that promised free internet calls for new users signing up for broadband.
Carphone Warehouse claimed that the calls were an inclusive part of BT's Total Broadband packages and insisted that the ads were misleading.
"The ASA considered that the internet phone calls were an inclusive part of that new package and that they should therefore not be described as 'free'," said the ASA verdict that upheld the Carphone Warehouse complaint.
The watchdog found that the BT adverts breached the CAP Code on 'truthfulness' and 'free offers' and told the company not to refer to its included internet calls as 'free'.
Meanwhile, an NTL tele-shopping broadcast offering 1Mb broadband has been cleared of its main claim by the ASA.
One viewer complained that describing the service as 'super-fast' was misleading because there were faster services available.
The viewer also complained that, although the ad was shown throughout the evening, the telephone number switched to an answering machine outside office hours.
The ASA also challenged whether the offer was still valid when the ad was on air, because the scrolling text gave a closing date of several weeks earlier.
In its response to the complaint, NTL said that 'super-fast' was not used as a superlative, and there was no expressed or implied claim that 1Mb was the fastest or the only broadband speed available.
The company also said that the only speed comparison mentioned in the ad was with dial-up, and that 1Mb broadband was many times faster.
As for the other claims, NTL said that it had now changed the ad to include the opening hours of its call centres and had corrected a fault where the channel displayed an old set of terms and conditions.
The ASA cleared NTL over its broadband speed claims, because it had not claimed to be the fastest service available.
However, the ASA upheld complaints that the offices were closed despite inviting viewers to join 'now', and that the closing date broadcast was wrong for several weeks.
The ASA told NTL to ensure that future ads gave the correct information.
Insecticides based on sulfoxaflor might be as bad for bees as neonicotinoids
Intel teases forthcoming new graphics card accompanied by the text "We will set our graphics free"
Think your password manager is completely secure? Think again...
ARM plans 7nm 'Deimos' for 2019 and 5nm and 7nm 'Hercules' for 2020