I can't say for sure, but my guess is no. Maybe if the voice was pay as you go but I can't see this split happening on one device. Interesting question.
Best bet is to call. If the person says they aren't sure, ask to speak to someone in next level. Don't be pushy, just ask nicely. In unique situations, some people might not bother to ask around and just flat out say no.
I doubt you could do that. Perhaps your employer would reimburse you for the phone portion of the bill. One employer I worked for gave me the choice of a phone provided by them or pay me for using my own phone.