[round-up of what has been written elsewhere about these quality cables]
Several kitizens have found these rj11-rj11 cables to be very good. I would strongly recommend giving them a try:
http://www.tandyonline.co.uk/high-speed-rj11-dsl-cable-1m.htmlthey are shielded and available in longer and v. short lengths (incl 0.5m) not just the 1m one shown above. Obviously shortest is best.
The products used to be known as
AdslNation (adslnation.com), and the shop is now labelled
Tandy.
They appear to be real copper, unlike some of the similar-looking cables (incl. inferior cable from kenable) which are aluminium, or aluminium-with-cooper-coating.
* The adslnation cables have metal bodied plugs, unlike the inferior varieties. I see a wire coming up the side of the plug, and speculate that this might be a drain wire for the shielding/braiding.
Q.: Is this possible/sensible? It would only make sense if the supposed drain wire were connected through the socket body to either an earth or at least to the shielding in the case of the modem.
Burakkucat has pointed out that shielding ideally ought to be grounded. On some of the cables of this type there seems to be no possible way to facilitate this.
One kitizen, AlecR, has had superior results with the Mr Telephones cable made out of Cat6 cable - see ebay. (I myself, and one other kitizen, have had performance and quality problems with this supplier, so test carefully.)
I've recently had an incredibly bad experience due to poor RJ-11 cables killing performance, so that taught me that good cables are critical, on weak signal lines anyway.