Since GrandCentral doesn't handle incoming SMS/text messages, it's a problem trying to decide how to represent one's phone contact information on, say, a business card or an email signature.
People are conditioned to understand O[ffice], W[ork], C[ell], and (maybe) M[obile] as prefixes for phone numbers on cards and email signatures.
I suppose one could use H[ome], but it's so uncommon a card or a sig[nature] that it doesn't make real sense to include it with the others. The common usuage would be to spell it out in a personal note or, perhaps, trade in a vCard.
If I were to use GC, for GrandCentral or U[nified], it would just cause confusion.
And dividing between V[oice] and T[ext] and labeling as such doesn't seem practical (and exposes a changeable cell/mobile number, too).