The best would be get an account from one the many bulk service providers, they should be cheaper, than the GSM Modem option, cause in a GSM Modem you need to insert a SIM and that will be charged for the SMSes you send.
Just google "bulk sms service providers" and you should get a pretty long list of them.
And depending on the provider he might give you a HTTP Link or an SMPP account or both.
i need to do a project on bulk sms.
i request you to send
java application for sending bulk sms from pc to mobile
I think the idea of it being your project is that you should make the application, not rip someone's hard work for your marks (if its an academic project) or money (if you are doing it commercially).
You have in this thread what you need to start making your own application, if you run into any road blocks you can definitely count on the people in this community to help out, but only if you put in the effort.