According to this source: jeziorki.blog spot.com/2012/07/modlin-airport-connected-by-rail-but.html (no space in blog spot word, but the entire url is being blocked here apparently) the rail link to/from Modlin rail station is functioning already (+ free bus ride to the airport).
As of Friday, 29 June, one can travel to Warsaw's new airport at Modlin by train. According to rozklad.pkp.pl, the service operates around the clock, which is useful, as check-in for WizzAir's popular 6:00 departure to 'London' Luton opens at 4am. The airport's
press release mentions a bus service, coordinated with the train arrivals and departures, to take passengers on to the airport. There's a train arriving at Modlin station at 3:20 and the next at 3:51. A bit of an all-nighter then.