Apple's first folding phone, the iPhone Duo, hit stores around the world on Friday with a price tag of about $2,000 and less of the fanfare that accompanied previous iPhone launches. From Singapore and Shanghai to London and Berlin, demand was strong but with sales rationed, there were fewer of the round-the-block ?queues and overnight camp-outs that once marked new iPhone days.Competitors such as Samsung Electronics and Huawei Technologies have sold premium foldable phones for years and the Duo is a test of whether Apple can reinvent the small foldable mobile market the way the iPhone did for smartphones. It…