Beyond being limited to the one phone, you'll have to stick to some of its preloaded apps, including the browser, contacts, email client, photo gallery, Polaris Office and S Note.

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But with some other administrators (and to buy individual stocks through Fidelity) you have to get online or on the phone to move new money into out-of-plan investments.

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"We did envision that some day the phone would be so small that you could hang it on your ear or even have it embedded under your skin, " he said.

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If you get your boarding pass on your phone, some airlines can update it if your seat or flight changes so you don't have to stand in line at a kiosk or counter.

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