Wideband CDMA is a third-generation (3G) wireless standard which utilizes one 5 MHz channel for both voice and data, initially offering data speeds up to 384 Kbps. WCDMA was the 3G technology used in the US by AT&T and T-Mobile.
There are several newer upgrades to WCDMA that offer much faster data speeds, such as HSDPA and HSPA+. These do not replace WCDMA, but rather build on and enhance WCDMA. Therefore any phone with HSDPA or HSPA+ also includes WCDMA by definition.
WCDMA is also referred to as UMTS - the two terms are effectively interchangeable.
WCDMA is the standard that most GSM carriers moved to when upgrading to 3G. Parts of the WCDMA standard are based on GSM technology. WCDMA networks are designed to integrate with GSM networks at certain levels. Most WCDMA phones include GSM as well, for backward compatibility.
WCDMA borrows certain technology ideas from CDMA, as the name implies, but is in fact very different and incompatible with phones and networks using "CDMA" technology.
In Europe and Asia, WCDMA was first deployed in the all-new 2100 MHz frequency band. In North America, WCDMA was deployed in the existing 1900 MHz (PCS) and 850 MHz (cellular) bands, as well as the newer 1700 MHz (AWS) band.