There is limited quota to perform yatra for yatrees holding Indian passport whereas there is no quota system for other nationalities – there is quota enhancement discussion in progress between Pak and India and hopefully there would be soon some positive decisions in this regard.
It is advised to start visa processing well advance (at least two months) before setting off yatra tour – one may apply yatra visa even without Pakistan sponsor but it is always better to have proper sponsor letter from your Pakistan counter-part that would be helpful for the embassy for smooth processing.
If you are on status of residence permit with Indian passport in any foreign country other than India and want to cross Wahga Border by road then you need to get endorsed on your passport (crossing border by foot etc) by the Pak embassy where you apply visa that would allow you to enter Pakistan through your private means of transport – no need extra endorsement on passport if by air. Residents of Europe, America, Canada or nationalities having passports other than India may enter without such endorsements. For latest information you may contact with nearest Pakistan Embassy or Consulate.