Centralise Registration of Service Tax

How can I do Centralise Registration of Service Tax?
"There are 3 branches of the company viz, Mumbai, Kolkata & Bangalore"
Mumbai & Kolkata has two different Service Tax Numbers
while Bangalore is not yet registered for Service Tax
How can I proceed for centralise Registration of all three branches ?
What are the documents needed?
What is the processing Charges?
Where(address) should I go for submitting the documents?
What time can I expect to get  the Registration number ?
Should I use Mumbai & Kolkata  Service tax numbers from application date till the time I will receive the centralize  number?
 

RGDS,

RAJANI