Whether Input of service tax is available or not

Prior to statuary liability of service tax for providing services, input credit is not possible. 

Mobile bills are not input services, hence input credit not available.

I disagree with Mr. Sharma on the grounds that since ST. has been chargd by the telecom service provider it shall qualify as input Service Tax

to avail the input credit on telephone bills, the should be 

1) in the premises of service providing address, or

2) used by the person ( workers) providing the service

3) such telephone is needed in row to provide the service

4) such telephone must be in name of the FIRM, or assessee

if assessee have mobile phones for use in residence and for field work of staff, it does not qualify as input service for providing taxable output service, for claiming input credit the nexus between input services and out put services is must.

If one is provding the taxable service liable to ST prior to the date of registration, the eleigible credit would be available as set off while paying the ST on the output services along with interest thereon.

There is no bar in availing cenvat credit in relation to input service received prior to registration provided other conditions are fulfilled.
 

what are the other conditions????