While some of the girls start out on their own, the majority of them enter after coming into contact with a pimp.
When a new girl enters any den, the incumbent workers show her the ropes and how to behave with the house clients.
Besides Bengali girls, women from the Central Asian States, Bosnia, Afghanistan and Burma can also be found marketing themselves in the capital.
Until the late 1970s - when General Zia-ul-Haq embarked upon a drive to "Islamise" Pakistani society, closing down brothels to the public, red light areas - as a legacy of British rule - continued to be institutionalised.
A local sociologist explains: “With the closure of brothels to the public, the prostitutes - whose profession is often passed from generation to generation - dispersed to the cities’ residential areas to earn their livelihoods.
In the initial years, Shamim had to work very hard not only for herself but also in order to cultivate enough contacts to begin her own operations with at least five girls in her employ.
Soon after she entered the world of commercial sex, Shamim bought herself a mobile phone and circulated her number among her clients.
As an independent Muslim state, Pakistan does not officially allow prostitution.
Unofficially, however, the practice is prevalent all over the country, with the majority of the clientele ironically comprised of politicians, bureaucrats, police officials and army personnel; in short, the very people who are supposed to legislate and implement laws against the sex trade.In return, pimps provide police protection, shelter, and bear their day-to-day expenses, including food and cigarettes.A young call girl from Sahiwal, said: “My parents have "rented" me out for three months to Goga Bhai (a high-profile pimp in Karachi) for one lakh rupees (100,000).” However, she says has no complaints about living with the man because she is treated well.It becomes hard for her to meet even her monthly expenses.Those with dancing skills, however, have some bonus years in which to attract customers in this marketplace."The most astute call girls in Karachi work in tandem with their pimps for between six to eight months, after which time they strike out on their own to become suppliers. A one time call girl, she is today one of the best-known pimps in Karachi’s higher social strata.As economic recession in the country deepens, many girls from different parts of Pakistan are thronging to Karachi where the market is comparatively better than in other nearby regions.