Not at all. I have an MCI toll free number that points to my Sprint PCS phone, and have had no problems with it. All that's needed is to give your PCS number to MCI as the "ring to" number, and you're set.
FYI, mobile-to-mobile calls will not be billed as such if the other person calls your toll free number, because the call is being routed off the Sprint network and then back on to it. So if you have unlimited PCS to PCS calls, be sure the other party calls your cell number, and not the toll free number.
E-mail fudged to thwart spammers. Transpose the c's and a's in my e-mail address to reply.[TELECOM Digest Editor's Note: I have a toll-free 800 number pointed to my regular number, but in order to know *who is paying for the call* and partly to select the correct answer phrase, I have it ring in on a distinctive (ring-ring) line, as opposed to just my regular line. If I hear that ring-ring, I know it is a call on the 800 line, or just a wrong number dialed in on the distinctive number. PAT]