Thanks for a wide variety of replies to this! Some very good points raised and so let me summarise with some additional information thrown in for good measure.
What do you need your phone for
If you don't need to use your phone while out and about then just stick it in either a sealable plastic bag or, for those situations where a greater degree of protection is need, a pelican case. Storing it switched off should mean that the battery is useable when you switch it on.
Durability, battery life, talk time and standy time
Of course if you are using your phone while out and about, or of you do need to use your phone in an emergency then the durability and the battery life become important factors. I'll cover this more later, but it is worth noting that battery life is tested in ideal conditions and will be dramatically shorter in cold conditions and areas where the signal is poor. Similarly, how tough the phone needs to be depends largely on where/how you will be using it. It may seem odd, but sometimes an object designed and billed as being tough can break long before an "ordinary" object. Why? The "tough" item gets abused where the "ordinary" item is taken care of. Just because something is tough or "safe" doesn't mean it should be abused. In my professional life I have seen the results of someone acting dangerously because of a mistaken belief that the safety equipement will prevent all harm.
Compatibility with solar chargers
I haven't looked into this yet ... but I would expect that any of the solar charger systems out there would be compatible with the main brands of phones. Anyone care to comment?
Emergency calls
Ihave never tried this but I know that even when the keypad on almost every phone I've ever had was locked, it was still possible to dial 999 or 112 and connect to the emergency services even when off contract. I dug out an old SE phone locked to Orange and without a SIM and started dialing 999 ... it came up with "Emergency call" (note: I didn't complete the connection!). So if all you are looking for is a last ditch backup (you've already constructed a signal fire, right?) and you are prepared to risk not having any signal foiling your plan, then carrying an old SIM free phone in a waterproof plastic bag will save you some money on monthly contracts or keeping PAYG topped up.
The contenders
There was a list of suggestions from people (thanks folks). Many of them are out of prodcution or have been superceeded by new models so I'm not going to look at them here. However I've prepared a table showing some options and how they stack up on the essentials:
Make/Model--------------Size (mm)--------------Weight (g)--------------Talk time (hr)--------------Standby time (hr)--------------Dual/Triband--------------IP54--------------Price (SIM Free)
JCB Tough Phone-------113 x 50 x 22--------------150-----------------------------4-----------------------------200-----------------------------------Tri-----------------------------Yes------------------------£190
Nokia 5140i----------------107 x 47 x 24--------------101-----------------------------2-----------------------------150-----------------------------------Tri------------------------------No-------------------------£105
Sonim XP1------------------113 x 50 x 22--------------150-----------------------------4-----------------------------200-----------------------------------Tri-----------------------------Yes------------------------£235
Samsung M110 Solid-109 x 48 x 17.9--------------95----------------------------8-------------------------------400---------------------------------Dual---------------------------Yes-----------------------£80
Nokia 5500-----------------107 x 45 x 18--------------103-----------------------------4-----------------------------270-----------------------------------Tri-----------------------------No-------------------------£135
User experience and other comments
Despite the marleting of the JCB Tough Phone and the Sonim XP1 (the JCB is a branded XP1)there are a surprising number of reports out there of the phone breaking very easily or having software/hardware problems unconnected to any physical damage. Certainly enough for me to be cautious about this phone. Certainly the higher price of the XP1 is odd .... perhaps JCBs marketing strategy is different.
Nokias are old favourites of many and are probably very reliable, but the talk time and standby time of the 5140i is disappointing. Fine as a backup but maybe not so good for those needing to use thier phones while out for any length of time. the 5500 seems tough and reliable.
The Samsung looks like a good option. Certainly the cheapest of the bunch, small and light and with great talk time and stanby (way ahead of the others), it is let down by only being Dual band rather than Tri band ... but this is ONLY an issue for those heading to places like North America, within Europe and many other regions it will be just fine.
