The roaming is a possibility between the GSM and CDMA networks and in some networks in SE asia, trials are on. Basically this requires the CDMA handsets to be equipped with R-UIM (similar to the SIM cards in GSM) and some other support as the reciever. On the core network side there is an additional component called Network Interface controller (NIC) that helps in authentication. This is still in very primitive stage and a lot needs to happen.
On the second query, there is no CDMA 3X or WCDMA in CDMA world now. UMTS, WDMA, GSM 3G all refer to one of the same thing where access technology is CDMA (with 5MHz carrier) and core is GSM.
The CDMA will not go to CDMA 3X (or WCDMA). After CDMA 1X there is 1X-EVDO and then 1X-EVDV.
so the dream of consolidation of GSM and CDMA network is quite far. Unless some good results come outof these trial, we need to wait till 4G.