Monthly Archives: January 2019

Everything you never knew you wanted to know about phone numbers

A couple of months ago, a number of my friends were surprised to encounter a “landline” phone number (01865 …) which, when called, got through to someone on a mobile phone. So I was inspired to write up a bit about the technology behind that and how it’s easier and cheaper than you think it is.

Here are some fun facts about phone numbers (I live in the UK, and most of these are UK-specific).

  1. 07 doesn’t necessarily mean mobile. Yes, there’s a fair chance that a UK phone number starting with 07 will have somebody’s mobile (or voicemail) on the other end of it, but it is perfectly possible to buy 07 numbers which have no device/SIM card attached to them and simply direct calls to other numbers.
  2. 01/02 doesn’t necessarily mean landline. Analogous to the above, while it’s a fair bet than an 01x or 02x UK phone number corresponds to a physical piece of copper with one or more telephone handsets on the other end of it, that doesn’t have to be the case. And even if it is, your call could be diverted to somewhere else entirely by the recipient’s equipment (at their cost). It’s especially important to know that, because of this, a business publishing a number with a certain area code is no longer a guarantee that they are actually based in that area.
  3. You don’t have to have voicemail on your mobile. If you’re as annoyed as I used to be with people leaving ten second voicemails identifying themselves when you already knew from the “missed calls” list and caller ID who they were, then you can usually ask your mobile phone operator to disable voicemail on your mobile. I don’t miss it.
  4. 03 means “non-geographic”. Because pricing of 08xx numbers in the UK is complicated, numbers beginning with 03 were introduced for use in company/government settings where a nationwide number is needed, and should have similar cost to a normal national call to 01/02. Most mobile and landline packages treat 03 the same as national calls to 01/02
  5. “Virtual” phone numbers are surprisingly affordable. As I’ve blogged here before, I run an 07xx number which we program each week to divert calls to whoever is leading that week’s walk for the Ramblers. It has a fixed cost of around £14 per year, plus a per-minute cost for the forwarded calls. Last year it cost us less than £20 in total.
  6. Caller ID should no longer cost money in the UK. The telecoms regulator Ofcom ruled last year that Caller ID on landlines should no longer be a chargeable extra (given that it’s been a standard facility of the network for decades now, charging more for not turning it off seemed dubious to me for quite a while). Given this, all you need is a landline phone handset modern enough to have a display, and you can see who’s calling you. If you’ve ever wondered why it takes one ring before the ID shows up, it’s because it is transmitted as a modem-like series of sounds after the first ring (as long as you don’t pick up very quickly).
  7. 17070 can be useful. If you want a UK landline to read back its own number to you, most networks allow you to get this by dialing 17070, an engineers’ test facility which should be free and work even on stopped/suspended lines e.g. when you’re moving into a property – as long as it has a dial tone, 17070 should work.
  8. You can “call” people using Facebook Messenger, WhatsApp or Signal. Look carefully at the interfaces in these apps, and you’ll see the option to call people using them. The advantage of this is that the call goes over the internet, so provided you are on a non-metered internet connection, it won’t cost you on a per-minute basis. This is especially useful when calling home from abroad (although, at least for another two months, EU roaming means UK citizens abroad in Europe can usually call home on their mobiles at the same cost as calling from within the UK).

tar pipe with nc, updated for 2019

If you’re a Linux user, you’re probably familiar with the so called tar pipe, a quick and dirty method for transferring files across the local network. It works, and it uses the most basic of tools. Indeed, if you want to shove a load of data between two Windows machines as a one-off, e.g. for a backup, I often find it quickest to boot them both from a Linux live CD / USB stick and use tar pipe (ntfs-3g to mount the disks, naturally). Much easier than trying to persuade file sharing to work properly.

My personal variant, on systemrescuecd:

sending end:~# tar cvf - * | nc receiving-end 1234

receiving end:~# nc -l -p 1234 | tar xv

The addition of v for verbose means you get a print out of files being sent and arriving, giving you a crude approximation of progress and a rough idea of when it’s finished.

It’s also worth noting that the connection provided by netcat is bidirectional (it’s just a TCP socket), so you can in fact establish it the other way round (which is handy if the receiving end is e.g. the Windows Subsystem For Linux, where the Windows firewall gets in the way of listening for an inbound connection):

sending end:~# tar cvf - * | nc -l -p 1234

receiving end:~# nc receiving-end 1234 | tar xv

SSD transplant: Windows 8

A disk I’d been keeping a concerned eye on for some time … now retired

As is traditional while staying with relatives at Christmas, I did some PC upgrades. I was much happier with the slightly venerable Lenovo desktop running Windows 8 once I’d swapped out its rather noisy/crunchy 1TB hard disk for a 250GB SSD I happened to have spare.

Either I’m getting better as I get older, or the tools are improving. Five minutes on Google suggested using ddrescue from SystemRescueCD, and I simply deleted the references to recovery partitions which were beyond the end of the original disk. By far the longest part of the job was taking a backup first.

I’ll do a separate post on how that backup was done, as it was also the fiddliest part of the operation.

Credit where credit’s due to Microsoft: although Windows refused to boot after the transplant (“A required device is inaccessible”), it did offer me safe mode, and rebooting from there restored normal service. No need for CDs or suchlike faff.