According to iPhoneClub, Apple and carriers are preparing to launch white iPhone 4 by next Wednesday,
April 27th. Inside a phone store called BelCompany in Netherelands, an internal memo has distibuted between store employees confimred that.
White iPhone 4 will be available with T-Mobile contract with both 16 GB and 32 GB.
Update: here's screenshot of the above mentioned Memo :