I have recently discovered a few interesting MVNO's (Mobile Virtual Network Operators).
First up is KrossMobile which claims to offer 150 mins and 100 texts to "any country" for £5. Their web site is currently broken and I've been unable to get a response from them via phone or email. Whether it's genuine or not, I have no idea.
http://www.krossmobile.co.uk.
Next up is Kontakt Mobile who claim to offer £20 of calling credit + 1GB of Internet for £5. Their standard rate is 8p per minute/text to uk & some other popular countries, so if the deal is as it seems, that should work out at 2p per minute/text.
http://www.kontaktmobile.co.uk.
Finally, The Co-Op have launched a mobile brand. The reason I'm including it here as "interesting" is because they only charge 8p per minute for 0843/0844/0845 numbers with a minimum charge of 1p.
http://www.thephone.coop/tariffs-and-bundles/KrossMobile runs on Three's network, Kontakt Mobile on Vodafone and The Co-Op on "EE" (I assume that doesn't include 4G).
dave