Coming away from the main subject a little, I think blessings are a great way to introduce people to religion for further benefit in the future. I mean after all who doesn't want something that is blessed. Many people believe in the supernatural and want protection, so a great way to do this is try blessing. After they get something blessed, they will want to learn more about the religion. It plants seeds of dharma, and the want to learn more. So in conclusion it is a great way, with no commitment to bring people closer to the dharma.
Now coming back to the mobile phone. For me i see little purpose in blessing a mobile phone, I feel that is is just an act to make money in most cases. Forgive me if this is harsh. But that is the only reason I see. If we took the example of a car, then I can see a bigger reason, because with cars accidents are likely to happen, thus the blessing can reduce the chance of an accident. But with a mobile phone I can't see much of a reason. Having said that I believe that the arguments previously listed are valid.