Suppose I want to send a message to mobile from my website across the world(irrespective of service provider),then what I need to do? Do I need to develope my qwn code or I just need to use the available services??

Also I would like to know if any type of mobile service exists??(for example message only,call only etc)

Thanks in advance.

you need to write a code and a GSM device like mobile with datacable ,when you write a text and press send button your code will connect to your mobile or GSM device which send the data to any network.

Can you suggest me some links,books about mobile communication(with servers)regarding above question?

You can register some website which provide the facility of mail marketing , you can send your text message by these site .