AC the news is full of 'hints' like "FBI, Telecoms Teamed to Breach Wiretap Laws" ( 01.21.10)
http://www.wired.com/2010/01/f...
FBI Seeking to Pay Telecoms to Store Records for Years and Provide Instant Access (07.18.07)
http://www.wired.com/2007/07/f...
FBI pressures Internet providers to install surveillance software (August 2, 2013)
http://www.cnet.com/news/fbi-p...
Also recall Communications Assistance for Law Enforcement Act http://en.wikipedia.org/wiki/C...
".... requiring that telecommunications carriers and manufacturers of telecommunications equipment modify and design their equipment, facilities, and services to ensure that they have built-in surveillance capabilities, allowing federal agencies to monitor all telephone, broadband internet, and VoIP traffic."
Its the local laws where the handsets are to be sold that matters. If you want to sell in say the USA, your "designed" aspect will have to be US wiretapping law friendly.

Not much the average consumer can do about wire tap friendly products built into tame telco approved hardware and software as offered globally.
You can code a software layer into your consumer device that offers really good quality encryption.
The problem is not so much a back door, trap door, just that every letter and number entered on the device is open to hardware logging by default by a gov activated telco layer..
A person is walking around with a gps becon, live mic, camera and plain text capturing device they 'trust' due to a thin top layer of very good code?
A one time pad system, air gapped to get the message out? A user no longer has real time joy but is then only offering location, who made the message, where it went, when and all the details about the device that sent the message.

AC the backdoor aspect is both national and international
"FBI Wants Backdoors in Facebook, Skype and Instant Messaging"
http://www.wired.com/2012/05/f...
".... drafted by the FBI, that would require social-networking sites and VoIP, instant messaging and e-mail providers to alter their code to make their products wiretap-friendly."
Then the world was given more details "Encrypted or not, Skype communications prove Ãoevitalà to NSA surveillance" May 14 2014
http://arstechnica.com/securit...
As for the "nobody on the inside has ever leaked out." aspect try http://cryptome.org/2013-info/...
The "inside" can now be understood by aspects like "Drug Agents Use Vast Phone Trove, Eclipsing N.S.A.Ã(TM)s"
http://www.nytimes.com/2013/09...
..."employees sit alongside Drug Enforcement Administration agents and local detectives and supply them with the phone data from as far back as 1987."
How past "parallel construction" and telco support will respond to any new "peer-to-peer and voice calling" will be interesting.
How did the US and UK get to past bespoke crypto telco hardware in the 1950's and beyond? Plain text always seemed to emerge just in time.

It depends on why the data was collected.
Globally the NSA and its friends collect it all.
If your telephone number is of interest, email, net use or social media use is of interest then its sorted, indexed, voice print is kept.
In the old days it was keywords, now its hops to people of interest and your own political, social activity and that of your friends or friends friends.
Your camera sensor pattern noise/noise signature, cell tracking, car...
Just the fact a person feels the need to use 'encrypted communications' found at a city, state, federal or international level makes them interesting.
The 'encrypted communications' would be kept, noted and the password looked for in past communications hinted at in IM or email.
if that fails and your still of interest - some form of key logger for the next time you encrypt or decrypt or open your application at keeps track of different passwords :)
An easy pattern might drop out of years of easy to find past passwords use that could be tested.
it really depends on who a person is, their friends, their friends of friends. Collect it all and sort is now the cheapest way of getting it all.

Yes some hints where given via the Martin and Mitchell defection in 1960 https://en.wikipedia.org/wiki/... too
"As we know from our previous experience working at N.S.A., the United States successfully reads the secure communications of more than forty nations, including its own allies."

Hi AC re "realistic hard number costs" would all be hidden over federal, gov and mil projects or just buying in bulk from the private sector.
Water and power usage at one site thats in the news is about all that can be worked back from.
"‘Black budget’ summary details U.S. spy network’s successes, failures and objectives" (August 29, 2013)
http://www.washingtonpost.com/...
hints at "$52.6 billion “black budget” for fiscal 2013" but that could be for very limited number for US internal consumption over a subset of mil/gov projects.
ie the US gov gets all domestic data thanks to tame telcos. The costs of storing aspects of every call would be small over decades as the above linked DEA news showed.

That local Fusion center https://en.wikipedia.org/wiki/... will help move real world local private/public data up to the federal level :)

You saw the DEA do it with phone call records.
http://arstechnica.com/tech-po... Sept 4 2013
".... to place its employees in drug-fighting units around the country. Those employees sit alongside Drug Enforcement Administration agents and local detectives and supply them with the phone data from as far back as 1987.""
Thats just one tiny project with once set of data.
Water news http://arstechnica.com/tech-po...
Power news http://www.zerohedge.com/news/...
Thats just for one classic storage site thats in the news a lot.
Re So what would it really take to put this sort of thing together?
"The ultimate goal of the NSA is total population control" 11 July 2014
http://www.theguardian.com/com...
"At least 80% of all audio calls, not just metadata, are recorded and stored in the US, says whistleblower William Binney – that's a 'totalitarian mentality'"
Should give an average reader an idea of the US internal scale to store, track, index, search, voice print, call to, call from, other numbers, work back from hops surrounding people of interest.
ie well funded, all of the USA, over years, aspects of calls stored for years ready to be found in storage if seen at a protest, near a protest or near a person who was near a person at a protest.
ie you just need a lot of tame Room 641A like access https://en.wikipedia.org/wiki/...

It gets and keeps the funding. Binney: 'The NSA's main motives: power and money' (19.08.2014)
http://www.dw.de/binney-the-ns...
"When you do the things that they do - dictionary select, like a Google query, you throw a bunch of words in and get a return. And if you do that for terrorism, you get everything in the haystack that has those words. So now you're buried - by orders of magnitude worse than you used to be. So you don't find them."
.... "Money. It takes a lot of money, you have to build up Bluffdale [the location of the NSA's data storage center, in Utah] to store all the data. If you collect all the data, you've got to store it, you have to hire more people to analyze it, you have to hire more contractors, managers to manage the flow. You have to start a big data initiative. It's an empire."
William Binney https://en.wikipedia.org/wiki/...
Its all about growing the NSA beyond its 1990's position in the US gov. No more just working to provide data to other mil and gov tasks.
The NSA seeks to run its own missions and be seen getting results, more funding and more political access.

Back to use once number pads, face to face and number stations. Takes a bit longer.

Also even if your phone cant get a good gps, it might get a location for other phones that can, in the area on the same networks.
Global Wi-Fi, cell-id location databases, ambient signals, visitors use gets a gov/mil some nice indoor positioning.

The UK made sure a kind of early tracking tech was ready for cell phones as a standard due to experiences in Ireland back in the day. Not unexpected news back then, a strange story to make Slashdot in 2014.

Dont unpack and test your new phone near your everyday phone. If it is your home, hotel room or work, every phone that is was normally in the area is now of interest due to that one time test activation. Numbers called, callers and voice prints will find that new interesting phone later and allow a gov/mil to work back.
If that does not work, just map an area where tow phones walk towards each other and turn/power off and turn on again walking away from each other.
Any phone is a risk.

Dual missions and attracting the next generations to gov, mil work and onion routing.
From collect it all reality to 'help' spread democracy branding.
If US backed dissidents face a new range of telco tools that are just been sold to govs, better to help developers stay one step ahead.
If a new range of telco tools used by the US govs to collect it all are just been upgraded, better to give developers some busy work for a few years.
Both options need clean social engineering access to real people to shape software directions over decades.

It depends on the US or UK mission. If the US gov wants to support some NGO doing a Colour revolution http://en.wikipedia.org/wiki/C... then the communications and support has to work well over years.
For every other use of online anonymity the US and UK would like to have a way in as now understood with most of the tame telco and banking crypto over decades.
e.g. NSA surveillance: A guide to staying secure http://www.theguardian.com/wor... (6 September 2013)
the classic line "... have invested in enormous programs to automatically collect and analyse network traffic"
The US gov and mil can afford do both and keep users guessing. Protect the very well supported "freedom fighters" just enough globally and still collect it all.