OK I found this article
http://abcnews.go.com/Health/ReproductiveHealth/Story?id=4890097&page=1I dont know if it's 100% safe or not but I wouldn't wear the cell phone on my waist while being pregnant or not. cause a while back I read an other article that said that women shouldn't wear cell phones in their waist cause they can lead to ovarian cancer or fertility problems.
hope it helps