IN A FEW YEARS, YOUR DESK-top phone may lose its cord. Today, cellular office-phone systems are rare due to their high operating expense. But cell-phone suppliers are starting to come up with differential pricing schemes, with calls made from an office being nearly free.

In the vision of Sweden's L.M. Ericsson, a set of channels is designated for in-building use. Calls would be picked up by an antenna in the building and relayed to the wired network. The same channels could be used simultaneously in dozens of other buildings because the signals are low-power and will not interfere with each other. Walk outside during a conversation, however, and the system would switch to a channel for long-range calls--with the charges mounting accordingly.

Telia Mobitel, the No.1 mobile-phone operator in Sweden, recently began testing a tiered pricing plan in cooperation with Ericsson. Some 27% of all Swedes already have mobile phones. Telia hopes the availability of cheap in-building use will nudge the subscription rate past 50%.

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