Sim only deals are available in various money amounts and the choice is yours as to how much money you want to put on your phone. There are many deals that you can look through to find the one that is right for you, that fits your needs. You can find a deal that offers six-hundred minutes cross network with texts that are unlimited to all mobile networks.  There are also deals with 500MB of data and mobile internet can also be included. 

There are budget deals that give you options like a choice between unlimited landline or O2 calls. If you do an online search you will find codes that you use to take advantage of the special deals for certain months. Sim only contracts can are listed by name, like T-Mobile, Virgin Sim only deals, unlimited text Sim only and Vodafone Sim only deals to name just a few. 

This is a monthly contract that is short term where you purchase a sim card only but not a mobile phone. This way you can keep the phone you have and your phone number and pay less for a phone plan that is a long term contract.  You save money by going this way since a phone is not part of the deal as you are only buying the Sim package.