This is Leicestershire --A man tricked British Telecom out of more than £12,000 by changing his name 19 times.
Darlington Chapangara (33), was living at the same address for five years when he used a string of false identities.
He also managed to fool British Gas, which he owed nearly £1,300, Leicester Crown Court was told.
Recorder Roger Evans said it was "shocking" BT had not followed up the discrepancies and "bizarre" no identity checks were made.
Criticising BT and British Gas, he said: "They're extremely vulnerable due to their own failure to take any precautions."
The scam only came to light when police arrested Chapangara on an unrelated matter and noticed a large number of documents relating to 19 different BT accounts, with unpaid bills amounting to £12,074.
Chapangara, of Scalpay Close, Beaumont Leys, Leicester, carried out similar trickery with British Gas, obtaining £1,293 of electricity.
Sentencing Chapangara to eight months imprisonment, Recorder Evans said: "You took advantage of the very considerable ease and convenience of the public to transfer utility accounts, to change one name to another. It's a facility which benefits many.
"It's startling you were able to change into a whole series of false names with utility companies.
"BT sat by and £12,000 went unpaid without anyone intervening. It was only when the police issued a warrant it was brought to anyone's attention."
Chapangara pleaded guilty to two counts of dishonestly obtaining telephone and broadband services from BT, by purporting to be someone else, between December 2007 to October 2012.
He also admitted dishonestly obtaining electricity during a similar period.
David Lee, prosecuting, told Leicester Crown Court: "In the end, it's other users who are paying the extra amount of money that wasn't collected."
Mr Lee said: "He committed various frauds by changing the name of the people in whose name the services should be supplied. It involved multiple accounts.
"There were other service companies also used from time to time."
Some of the people whose names were used, and who were inconvenienced by the scam, were known to Chapangara and others cannot be traced. One woman who had her passport stolen by an unknown person in Nottingham had her name used in the scam, but she now lives in Singapore and did not initially know anything about it.
Mr Lee said: "There's no evidence from BT or British Gas they asked to see any identification documents."
Sam Mainds, mitigating, said: "It's not appropriate to raise any mitigation in the way these offences were committed."
Chapangara's sentence is to run concurrently with a four-and-a-half-year sentence he is already serving for an unrelated offence of grievous bodily harm. Reported by This is 3 days ago.