Modern digital cell phones share channels -- a cell site can service dozens of phones on a single channel. Whether this is practical for your application is questionable, however.
For digital cell communications, the phone digitizes the speech and transmits the data in short bursts, tens of times a second. The return transmission to the phone is handled similarly.
Each burst contains either the data since the last burst, or enough data to last until the next, when the sound is re-rendered to real time. Since the transmission burst is a tiny fraction of the real time duration of the sound it encodes, this allows multiplexing on a time-sharing basis of, in the maximum case, many more than a dozen cell phones on a single tower channel.
The technology to do this, unfortunately, is expensive, and represents decades of research in digital voice transmission. Further, parts of it are still covered by patents, so you can't just buy hardware that does this job (at least not at this level).
One way you might be able to emulate this, however, would be to use VOIP software. Skype is a well known example that handles conferencing well (especially if you don't try to conference video, but voice only). You'd need one VOIP device for each sensor site, and a continuous connection (ethernet, wifi, or connect through the internet cloud -- some software will work without a central server, some requires it), then set up a conference. How well this would work over the long term (say, more than an hour or two) is a question left to the experimenter...