Network operators and mobile phone retailers have a tendency to promote tariffs that, but every now and then you find a real peach of a deal.
T-Mobile's MyFaves tariff, which is available from today, is a great deal if you call certain people very regularly, as it lets you choose five numbers every month and then call, text and MMS them as much as you like for free.
You can select any UK landline or mobile number, including mobile numbers from other networks, and at the end of the month if you want to change one of those numbers, you can. Very handy if you get dumped.
The MyFaves tariff starts at £25 and for that price you only get 25 minutes and 50 texts included -- so don't get this tariff if you're planning on calling people outside of the five pre-chosen numbers. Otherwise I strongly recommend checking it out.