How Do I Use Sms Service For All Employee

i am developing a web site for my organization ,there are above nearly 1000 employees, we are also manage our employee status and duty on daily bases, and all these record and duties are being save in one sql table,now we want that base on last record of each employee we have send sms to that employee via cellphone,and each employee has different cellular companies.
what is best way to to handle these requirements??