As she was dosing off, she was startled by the shrill tone of her mobile phone. The ringing continued, till she decided to answer it, in case it was an emergency.

She looked at the display screen, which read "unknown number". Nevertheless, she picked it up, her heart skipping a beat, dreading that it might be some unpleasant news from a friend or relative.

An unknown male voice, at the other end asked her how she was as soon as she answered the phone. Not identifying the voice, Shakila asked for his name and the purpose of his call. To this, he answered: "Shakila, I just want to be your friend and want to get to know you better."

Shakila realized instantly that this was a crank caller and told him that she did not talk to strangers.

The caller insisted on talking to her and at this point, she hung up. Within seconds, the man called her again. This time she answered the phone, screamed at him and hung up.

However, calls continued from the same number. Shakila turned off the volume on her phone and went to sleep. The caller did not give up, but continued to call her everyday, ever since.

"The person calls daily just after midnight. I have tried to tell him off a number of times, to which he called me vulgar names. He just does not want to take no as an answer," said Shakila.

Most teenagers and young girls like Shakila are burdened with the nagging problem of crank calls which has increased because of the "free calls within same operator" offer introduced by most mobile phone operators, complained these victims.

Users of a particular network can call another user of the same network from midnight to 8 am free of charge.

"We cannot sleep at night as most crank call come just after midnight," said Nahar, a student of Dhaka University. Nahar has been receiving calls from the same number for the last six months.

"Earlier, it was just 'missed calls' and at times, some vulgar short messages. That was not much of a problem. But recently, just after the offer came into operation, the calls regularly," she said.

Some users switch off their mobile phones during this period to avoid such nuisances.

"I switch it on, only when I need to make a call. Otherwise I always keep it switched off at night," said Arani, a private university student from Mohakhali, who also said that she, has had around six unknown callers daily.

"I usually turn down the volume of my phone. I may not get important and urgent calls if I switch it off," said Maleka, another mobile phone user.

These users are powerless, as customer care centres cannot help them regarding these problems.

"I kept on receiving calls at odd hours of the night, and immediately called the service provider. The calls stop for sometime and started again," said another user from Gulshan who did not want to be identified. She said that she had even complained to the police and since then, some callers stopped.

"If a user complains with details of the caller's number, times and dates, we do our best to take action to curb the nuisance," said an official from a customer care centre of one mobile operator.

"The 'action' is nothing more than just a short message from the operators asking the person to stop calling that particular number. This infuriates the caller and drive him to disturb us more," said Arani.

Some operators block the particular SIM, which is of little help.

"The caller can easily get another SIM and restart his pranks," said Polly, another victim of crank calls.

She suggested that the problem could be stopped, if the callers are traced and legal action taken against them.

"A victim would need to file a general diary against a particular number from which the crank calls are being made. We can begin to take legal action, once this requirement is met," said a police official, of Dhanmondi Police station, under the condition of anonymity.

But tracing these callers is a very tedious process, according to senior officials of mobile phone operators.

"Most of these subscribers are pre-paid users, who provide 'fake' details like addresses and contact numbers, when buying a SIM. As such, they are out of anyone's reach," said another senior official of a customer care centre, under the condition of anonymity.

Victims of crank calls are currently at the mercy of the operators, who are yet to devise a way by which these nuisances can be stopped, once and for all.