Not really. I made an assumption that the input power to the GSM pa is ~ 0 dBm, so the dBm/Hz and dBc/Hz is about the same. That's what I get for posting before my first couple of cups of coffee...
The specification you get from the GSM spec is at the PA output, and ends up being about -130 dBm/Hz. To determine the Phase noise at this input, you need to make some assumptions about the PA's gain and noise power, that's how you get back to a dBc/Hz spec, which is what the VCO guy's like.
Dave