Peter - are the mobile phone networks really reliable enough for this sort of use?
I'm sure we've all experienced random total loss of signal. Can last anything from a few seconds to a few hours. O2 recently had some very severe outages across the country, severe enough to make the press.
Signals also appear to degrade in poor weather.
are the mobile phone networks really reliable enough for this sort of use?
I think it's a very good solution.
GSM will never be as reliable as transmitting 15 watts on VHF from a few miles away 
But you don't have that option unless you have a frequency allocated. And with the frequency tax coming in... ?
I am not an expert on this but I think all SMS messages (non multimedia messages I mean) are sent via plain old GSM - regardless of whether the phone supports 3G.
As such (and could someone please correct me if I am wrong) they need only a very brief signal availability; far too brief to make a voice call or get internet ("mobile"; GPRS or 3G) data.
I have always found SMS to work below about 2000ft. In fact anytime the phone was showing a signal, it worked.
If SMS messages were ever sent over GPRS or 3G (which is an internet connection) then they could be highly unreliable.
Sure if your network is down then you are stuffed. In that case better to have a 2nd phone on a different network, and make sure any Caller ID in the receiver is configured to work with both.
There are other obvious methods (using some sort of RF signal, transmitted very briefly) which would be highly reliable but all would be technically illegal.
But you don't have that option unless you have a frequency allocated. And with the frequency tax coming in... ?
It can be done in an unlicensed band, and the hardware can be made simple and cheap enough to install a separate receiver in every light, the lights themselves being solar-powered. This way, you reduce the installation costs by eliminating all cabling (not much hardware investment but lots of labour, I'd say), and also make the system more reliable due to redundancy.
Would you get enough power from small solar panels?
The countless "garden ornament" solar powered lights seem to all be basically crap. You get a tiny glow from a little LED (which may be enough on a clear night) but the solar panels rot in no time from water ingress.
But I like the individual radio receiver idea
Does the frequency tax apply to receivers too?
Legally couldn't you use 135.475? You could specify a morse code for the pilots to tap in order to activate the lights, in order to avoid unwanted activations. e.g. '.-..' L for lights.
Would you get enough power from small solar panels? The countless "garden ornament" solar powered lights seem to all be basically crap. You get a tiny glow from a little LED (which may be enough on a clear night) but the solar panels rot in no time from water ingress.
One such panel per light would certainly be insufficient. I did some calculations a while ago, and about 8-10 of these would provide enough power for PCL meeting the official certification requirements for LIRL, etc., if you use high-efficiency LEDs. By the way, you get substantial power savings by creating the right directional pattern. For VFR lights you need a toroidal one, with most light radiated along the ground and only a little bit upwards; IFR lights can concentrate most light in a narrow beam along the glidepath (potentially both ways), with a fraction of intensity in other directions. These lights can be made completely sealed to prevent any water ingress. To prevent loss of performance from battery degradation (which will happen very fast in freezing weather), I would suggest using supercapacitors instead.
Good news: despite the persistent belief that pilot-controlled lighting does not exist in Europe, it actually does! As it turns out, Toussus-le-Noble LFPN has PCL with HIRL and PAPI, and operates unmanned at night, all arrivals to be reported to Le Bourget. Looks like it's now time to lobby for this thing to be propagated throughout the EU.
Both radio and SMS controlled - very nice.
Why do you believe one needs to allocate a frequency for PCL? The hardware at the airfield just receives on a frequency, it never transmits. This doesn't require any permission.
The sender is the pilot with his VHF and he is properly licensed to transmit on those frequencies. If one uses 123.45 MHz, there shouldn't be an issue.
