Beginning June 4, 2012, applicants who have applied for immigrant visas and have been found ineligible by a U.S. Consular Officer, will need to mail requests to waive certain grounds of inadmissibility directly to a U.S. Citizenship and Immigration Services (USCIS) Lockbox facility.
The U.S. Consulate in Islamabad will no longer permit applicants to come to the Consulate to drop-off their waiver documents after Friday, June 1, 2012.
Once you have received your immigrant visa, you must enter the United States within 6 months of visa issuance to obtain an alien registration receipt or "green card" (Form I-151 or I-551) that will allow you to live and work in the United States.
At the port of entry DHS officials will assign you an "alien number." They will stamp your passport with this number and make a notation that you are registered for an alien registration card. It normally takes several months for DHS to process and send the alien registration card to you.