It is a very common thing for the mobile companies to lock the mobile phones so that the user is restricted to use the SIM of only one network provider. Moreover, this locking might also be done to limit the use of the phone within a particular region or a country. Mobile manufacturing companies like Blackberry do this electronically into the system of the mobile phone. Locking is done only in those Blackberry phones that are handed over to the customers who are bound by various kinds of contracts with network providers.
One big reason to do this is that customers will then buy discounted mobile phones under contract from one network provider and start using the services of another one thus breaching the contract. The problem arises when you do not have another choice but to use your mobile phone on other network or if you have to go out of country and use the same locked phone, it will be impossible for you to do so. There is a solution to this problem. You can always get your mobile phone unlocked. If you want to unlock blackberry 9900, then you can always get a professional to do this after paying some small fee in return of his services.
There are other methods also which will enable you to use your locked phone on other networks. For example if you want to unlock blackberry 9810 then you can enter the unlocking code into the mobile phone and your phone will be ready to use in other networks or out of the limited area. The unlocking code is provided by the network provider upon request. If at all you are not furnished with the unlocking code by the network provider, you can go for alternative methods also. There are different software available that can be run in the mobile to unlock it. You can also do it by attaching the phone to some external hardware that will do the job electronically.
If you intend to unlock blackberry 9860 or any other mobile phone, you must take care of the number of times the code is entered into the mobile. The software in the mobile phones restricts the no. of attempts made by you to unlock it by entering the unlock code. This is just a means to check unauthorized unlocking of the mobile phone by random input of numbers in the mobile phone.