Here are the 10 top-selling smartphones for April by Philip Elmer-DeWitt @FortuneMagazine June 2, 2015, 11:15 AM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons Despite limited distribution, a relatively modest marketing campaign and the production complexities associated with making a curved screen, shipments of Samsung’s Galaxy S6 smartphones topped those of the Galaxy S5 over the same period last year and have nearly caught up to Apple’s iPhone 6 and 6 Plus. According to a report issued Tuesday by Hong Kong-based Counterpoint Research, Samsung in three weeks shipped 10 million S6 series smartphones to retailers in April, six million of which were sold. “‘We believe the Galaxy S6 Edge could have sold more if there weren’t supply issues,” said Counterpoint’s Neil Shah. “But it is on track to become more popular than the standard version as Samsung’s marketing engine kicks-in at full-speed.” According to Counterpoint, the Galaxy S6 series is mostly cannibalizing other Android phones, including Samsung’s. Apple’s iPhone 6 and 6 Plus in April remained the world’s No. 1 and No. 2 best-selling smartphones, shipping in volumes 51% higher than the iPhone 5S and 5C, according to Counterpoint. ‘The Samsung Galaxy S6 series has a chance to become the top selling smartphone overtaking Apple’s iPhone 6 series, if production issues are solved,” says Counterpoint research director Peter Richardson. “However the window of opportunity to do so is short as consumers don’t have much patience in a market with many alternatives.” Follow Philip Elmer-DeWitt on Twitter at @philiped. Read his Apple AAPL coverage at fortune.com/ped or subscribe via his RSS feed.