Some 8.7 million phone votes were cast
Adrian Rothery, from the west Midlands, told BBC News Online how his father-in-law was trying to call an ambulance when his wife, who is suffering from septicaemia, needed urgent hospital treatment.
Different family members, who all had phone lines with Telewest, could not make calls during the peak time for Pop Idol voting on Saturday night, Mr Rothery said.
Telewest has said that they did suffer congestion during that period, but that their network did not collapse.
Urgent
Mr Rothery said he was only able to make one call during that time and that was to a recorded Telewest message that said that any problems were likely to be due to high Pop Idol demand.
But attempts to get through to anyone else were unsuccessful until just after the ITV1 show's phone lines closed, he said.
"It was an emergency," Mr Rothery told BBC News Online.
"He was unable to call an ambulance, he was unable to call anybody in the family, so there was a two-hour delay before they could summon anybody."
Mr Rothery said his mother-in-law's life was never in danger, but that she was still in hospital and that her condition was "poorly".
Congestion
Telewest are now looking into the case.
"We did, of course, suffer from a phenomenal amount of telephone traffic on Saturday night, particularly at peak times," a spokeswoman for the firm said.
"There was congestion on the network, which meant that consumers may not have been able to get dialling tones.
"But the Telewest network did not crumble or anything like that."
More than eight million votes were registered on Saturday night - the largest ever amount for a UK phone poll - with reports that millions more people may not have been able to get through.
BT have said that they had to introduce an emergency "call gapping" measure to make sure their network did not go down.