Chelker - Emergency?
This park 'n' grab cache - or better - park 'n' hike cache, a camo-taped sample tube, is hidden at a lay-by on the A65 just north of Addingham village where you would park to do the excellent 6-cache The Chelker Walk series placed by fat bloke back in 2009 which takes you on a most enjoyable 2-hour walk over the high fields with great views throughout. This is a quick bonus cache to get you started!
Orange emergency roadside telephones (ERT) or SOS phones (thought to have been introduced in the UK in the early 1970s) are most commonly found on motorways (every 1.6 km with roadside markers indicating the nearer phone) but also next to hard-shoulders, lay-bys or junctions on other main (usually trunk) routes. They connect to traffic control centres or police control rooms.
The phones are marked by a placard or sign indicating a unique serial number or identifier which allows the authorities to know exactly where the caller is - even if the s/he does not know - by having the caller read the short identifier over the telephone.
When in full operation, there were over 6,500 ERTs throughout the UK.
Improving coverage of the cellular network together with high maintenance and upkeep costs have resulted in declining use of emergency telephones for highways and they are being gradually phased out.
The motoring organisations AA and RAC used to operate roadside telephones which could connect to the organisation's control centres for breakdowns, or police control for other emergencies. See here for a short article (with photos) on the 19 remaining examples of these in UK. Most of these have been removed or taken out of service, but some of the more modern phones are now operated by the trunk road agencies as normal ERTs.
Emergency phones can also be found at the ends of bridges or near cliffs which have a history of suicides. These are generally routed directly to appropriate support agencies such as The Samaritans. They are also occasionally found along the coastline connecting directly to the Coastguard where members of the public can report swimmers or boats in danger at sea. They are also found in lifts for use if entrapment occurs and connect to an operator who can help people escape.
In some countries, they are also commonly found where people may feel vulnerable or unsafe at night - 
such as university campuses, urban parks and housing estates. These are generally linked to security companies who patrol the streets where the phones are located.