issue with splitters on phone

I just installed the new Gig Modem with phone service. For the phone service, I needed to use a splitter to connect the phone service, one going to my wireless phone and one going to the wired system. After a short period of time, the phone stop working. I remove the the splitter and connect the lines on at time and they work. Install the splitter again and stops working. I have used 3 different splitters all having the same problem. The lines when plugged by themselves work fine, using the splitter, i have problem.  Also, I never had this problem with my old modem. ONLY this new one