When we started talking about mobile devices being the primary way that people connect to the Internet, we did not think the transformation would be so difficult for the leading device maker. At a conference in London on Wednesday, Nokia intends to present at least two new phones, one aimed at high-end users and one for the midrange mass market, people with knowledge of the presentation said. Time is not an ally for Nokia in the fast-moving smartphone segment of the mobile market, which now accounts for more than half of all cellphone sales in North America and Western Europe. For Nokia, the decision to abandon its own Symbian operating system in favor of Windows Phone came at a price. Operators quickly reduced their stocks of all Symbian devices, both smartphones and basic phones, hurting Nokia’s bread-and-butter business.