Question : Cisco IP-phones + WS-C2960-48PST-L POE

We are planning to purchase 48 Cisco IP-phones and WS-C2960-48PST-L, and connect 48 ip-phones to the one box, but  Following cco url states....  

"the Cisco Catalyst 2960-48PST-L configuration can deliver the necessary power to support 24 ports at 15.4W, 48 ports at 7.7W, or any combination in between "

https://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/product_data_sheet0900aecd80322c0c.html

The statement implies that we have to choose IP-phones that consumes less than 7.7W  each for maximum to utilize all the 48ports of Cat2960 to POE to IP-phones to work..
I just want to know which specific IP-phone product I should purchase, in order to make it work..

Answer : Cisco IP-phones + WS-C2960-48PST-L POE

With PoE, the phones will request the wattage that they need, so although it may vary as istvan says above, based on cable length, the rated power listed should be the MAX it will take with an in-spec copper run of no more than 100m (which is the Ethernet spec)....

Your assumption is correct - you need to make sure the combined wattage requested is not more than the switch can provide.  The switch will simply stop sending power, ignoring any new requests..  Those additional phones will remain unpowered...

The list of specs for the phones is available here:
http://www.cisco.com/en/US/products/hw/phones/ps379/products_data_sheets_list.html
but they really could make it easier..  If you see a phone listed as "class 2", that is a max of 7w..  Class 3 is 15.4 watts...

Here's a great link:
http://www.cisco.com/en/US/products/hw/phones/ps379/products_qanda_item09186a00808996f3.shtml

In there, you'll see  a GREAT list of Q&A about all of this, including this, which is what  you specifically asked for:

"CP-7902G (6.3W)
"CP-7905G (6.3W)
"CP-7910-SW (6.3W)
"CP-7910G (6.3W)
"CP-7912G (6.3W)
"CP-7940G (6.3W)
"CP-7960G (6.3W)
"CP-7906G (5W) (Class 2)
"CP-7911G (5W) (Class 2)
"CP-7941G (6.3W) (Class 2)
"CP-7941G-GE (12.9W) (Class 3)
"CP-7961G (6.3W) (Class 2)
"CP-7961G-GE (12.9W) (Class 3)
"CP-7970G (10.25W) (Class 3)
"CP-7971-G-GE (15.4W) (Class 3)
"CP-7985G (12.55W) (Class 0, Not full brightness)
"IEEE 802.3af Device - Class 0 (15.4W)
"IEEE 802.3af Device - Class 1 (4W)
"IEEE 802.3af Device - Class 2 (7W)
"IEEE 802.3af Device - Class 3 (15.4W)

Keep in mind, some phones are 802.3af power (standard) and some are "Cisco PRE-Standard"... Make sure your switch can provide the appropriate type of power for the phones you get!!

-Steve