UMTS vs WCDMA

I have a modem that uses UMTS & another that uses WCDMA. Is there any reason why the UMTS modem works at speeds up to HSDPA while the WCDMA modem is stuck on GSM? They are both using the same sim & connection dashboard. I am in Australia but I purchased the (unlocked) WCDMA modem in UK. Is there anything I can do to speed up the WCDMA modem?