In Urdu, words of Persian origin can take an "-aa" suffix to provide the vocative meaning, e.g. xudaayaa = O God, but it seems no where near as productive as the "-aa" suffix in Punjabi (munDiyaa = O boy, rabbaa = O Lord, Haafizaa = O Haafiz etc. There is also the particle "yaa" from Arabic, as in "yaa Allaah" (O God). This again is only used with very few words. The most frequent particle is "ai" (originially from Persian) as "ai dil mujhe aisii jagah le chal jahaaN ko'ii nah ho", ai laRke, ai laRkii. For Hindi I have heard "he bhagvaan" (O God). How often is this particle used? Is it fairly productive? Can anyone think of any film songs where "he" is used? What other vocative suffixes/particles do Hindi speakers use?