I am new here and not at geek status in the world of telephony but fascinated nonetheless of the possibilities that can drive us intelligently to the future, a harmonious dance between technology and man delivered safely and not to the detriment of the user of the tool, or tools we clad and surround ourselves with but are they all safe and if not who cares except for ourselves and our children also attracted to the appeal to connect easily and ubiquitously and that all great…if we minimise the risk and the cost to heal.
So how can we convert a mobile incoming signal to an old fashioned radio frequency like the old hands free sets connected to base we carried around the home…a retro move toward safer phone use via a cocktail of technologies old and new.
How to build this would be of great interest to me and I am sure many people who are becoming more aware of the risks of cell phone use.
If you are concerned about the near field transmit power of the old fashioned radio used by mobile phones, use a wired handsfree system (or even better, use one with acoustic tubes). In a car, use a non-contact hands free system and mount the mobile phone antenna outside the vehicle (may require a very old phone, as most phones no longer allow the substitution of an external antenna)…
If you must use low power radio, use a class 3 bluetooth headset. You may find these difficult to get as the market wants range, not low power.
Note that the main causes of mortality and morbidity from mobile phones are road traffic accidents caused by paying more attention to the conversation than the road. Whether exposure to old fashioned radio frequencies, such as mobile phones, causes problems is controversial and any effect is small compared with the road deaths cause by driver distraction by phones.
None of this has anything to do with Asterisk.
In the contexts where using a GSM terminal, PABX, and DECT phone would be an alternative, at least in the Western world, using a landline phone connection and loud-speaking phones would seem to be a better option, as cordless phones also generate RF power near the brain.
(Although I came up with the acoustic tube suggestion from first principles, a Google search indicates that there are acoustic tube products for mobile phones, although they tend to only use the acoustic tube for the ears - the microphone will be some distance from the brain,though,)
Hint: clearly specify the problem you are addressing. Most people do not consider your problem to be a problem. Also give specific benefits, rather than using phrases marketing type language.