The hard part here would be getting a RF subsystem with the kind of range you are talking about. As someone else has pointed out in another comment below, software radio is essentially applying a wideband analog-to-digital conversion, followed by software demodulation (bit like a winmodem, come to think of it).
To get the whole range from 0 to 2.4GHz or so sampled, you would need to be sampling at above 5Giga Samples per second (GSPS). Realistic sampling at least today is closer to few 10s of MSPS. Instead, what is typically done is to target a specific center frequency, say 910MHz, and sample at about 50MSPS around that. This means you need some other hardware that takes care of shifting the center freq to the right place, and this would reduce the utility according to how much you can afford here.
The real utility of Software Defined Radio would most likely at least initially be in places like base stations that have a legitimate reason to want to talk many protocols at once without adding hardware. Software defined handsets are less useful because of the power and cost.
Apart from all this, of course, privacy is still a separate issue - it depends on your encryption, not on the way the modulation is implemented.
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The hard part here would be getting a RF subsystem with the kind of range you are talking about. As someone else has pointed out in another comment below, software radio is essentially applying a wideband analog-to-digital conversion, followed by software demodulation (bit like a winmodem, come to think of it).
To get the whole range from 0 to 2.4GHz or so sampled, you would need to be sampling at above 5Giga Samples per second (GSPS). Realistic sampling at least today is closer to few 10s of MSPS. Instead, what is typically done is to target a specific center frequency, say 910MHz, and sample at about 50MSPS around that. This means you need some other hardware that takes care of shifting the center freq to the right place, and this would reduce the utility according to how much you can afford here.
The real utility of Software Defined Radio would most likely at least initially be in places like base stations that have a legitimate reason to want to talk many protocols at once without adding hardware. Software defined handsets are less useful because of the power and cost.
Apart from all this, of course, privacy is still a separate issue - it depends on your encryption, not on the way the modulation is implemented.