Some information here:
On pay monthly it appears:
http://www.virginmobi...ce.footer.sm068#Terms and conditions of service - Pay Monthly Contract
"4.8 Returns: If you have obtained your handset or SIM directly from us, for example, through our website www.virginmobile.co.uk, through a Virgin Media Store or by speaking to our Team then you will be entitled to benefit from any customer satisfaction guarantee and equipment warranty that we provide. Full details of such customer satisfaction guarantee and warranty are detailed in the joining pack you receive with your handset or SIM and are also available from our Team on request. If you have obtained your handset or SIM from another source, for example a high street retailer who may offer services from a variety of networks, any customer satisfaction guarantee and warranty that we provide will not be available to you. You should check directly with the retailer where you obtained your handset or SIM what their policy is should you wish to return the handset or SIM or if either of them develops a fault. If you do return your handset or SIM for any reason then you will be charged for any calls or use of our Services at the rates set out in our Tariff Table".