O2 Mobile Contracts are offering the HTC 7 Mozart Pay Monthly O2 Unlimited Contract with a monthly internet allowance of 1GB. The initial cost of the phone is £0.00. The monthly cost of the contract is £72.00. The contract lasts for 18 months. O2 offer a number of Bolt Ons which you can add to your contract such as the Family Bolt On, Data Top Up Bolt On, MMS Bolt On and the Data Abroad Bolt On.