The Pakistan Telecommunication Authority (PTA) said the ban was enforced last month due to protests from parents and lawmakers, but critics warn it is the latest attempt at creeping censorship.
The PTA first pulled the plug on dirt-cheap chat rates and late-night discounts in November, but operators simply started offering the services under different names.
So the regulator tightened the ban late last month, ordering telecommunication companies to scrap immediately "all kinds of chat services, irrespective of the time of day".
In a country, where parents keep young people on a tight leash and dating is considered inappropriate, late-night chatting over the phone or Internet can be a way to find love below the radar.
In Pakistan girls can be beaten or even killed by male relatives if there is any hint they are having a relationship and parents like to strictly control the marriages of their offspring.
A 20-year-old university student who did not want to give his name told AFP that the ban had hit him hard as he is now unable to chat with random girls and find new dates.
"The cruel world has once again conspired against lovers and made it difficult for them to communicate," he told AFP.
"It was so inexpensive and an easy way to find a date," he added.
The 25-year-old manager of a boutique in Islamabad told AFP that he had found the "love of his life" through the service.
"I am going to marry her," he said.
"We chatted, we exchanged numbers, we started talking and I was surprised to find out that she lived nearby," he said.
There is no public data about how many people used the romantic chat, but of the 68.6 percent of the population with access to a mobile phone, it is likely to have been a small number.
Normal call charges are about two rupees ($0.02) a minute and 1.50 rupees for a text message, but chat services were offered at an hourly rate for a fraction of those rates.
A customer would dial a particular number after which a computer generated voice or text message guided subscribers through various options.
For example, if you want to chat to a girl press 1, a boy press 2, then you select your preferred age group before being connected to another caller by SMS conforming to your criteria.
Two of Pakistan's five mobile phone companies said they had shut down romantic chat rooms, but would continue to offer calling services that stick to general interests such as hobbies.
Another company said they had shut down all chat rooms and two others were not reachable for comment.
Saeeda Khan, a 45-year-old mother of three, welcomed the ban.
"I am worried as they're busy all night on the phone with their friends and cousins," she told AFP.
Khan said she worried about "what kind of people" are in the chat rooms and that children "are exposed to strangers". "I would never approve of chatting with unknown people," she said.
Mobile phone companies have filed petitions in the Supreme Court against the ban, but no date has been set for a hearing.
Pakistan's oldest English-language newspaper Dawn has accused the PTA of acting as an "unwanted morality brigade".
"The intermingling of young men and women is not a matter that should concern the state which has nothing to gain except opprobrium by acting as self-appointed guardian of society's morals," Dawn wrote in an editorial earlier this month.
"It (the PTA) should mind its own business."
The PTA defends the move as a response to public anger, but the ban has raised fears about growing censorship in Pakistan.
The government frequently shuts down mobile networks to prevent militant attacks and access to YouTube has been blocked for a year over a low-budget American film deemed offensive to Islam.
In November 2011, the PTA also tried to ban nearly 1,700 "obscene" words from text messages, which included innocuous terms such as "lotion", "athlete's foot" and "idiot".
In 2010, Pakistan shut down Facebook for nearly two weeks over blasphemy and continues to restrict hundreds of online links.
Independent technology think-tank Bytes for All, Pakistan told AFP that the fresh ban was a violation of human rights.
"Any regulation on the basis of 'morals' falls under moral policing, which is unjustified, undemocratic, dictatorial and a violation of fundamental rights," Furhan Hussain, Coordinator Advocacy and Outreach at Bytes for All, Pakistan, told AFP.
One engineering graduate, when asked if he had ever used the chat service, said he regretted only hearing about it after the ban.
"Damn! I could have been dating girls, now I regret it."
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