Data from an arduino to be transferred to COSM through wireless internet
Given the constraints specified in the question, here are a couple of data communication options:


Zigbee module connected to the Arduino, in End Device mode, another Zigbee module in Coordinator mode on a PC connected to the wired network: 802.15.4 protocol, 250 Kbps speed (2.4 GHz modules), 10 to 50 meters range, 75 meters if you are lucky
Bluetooth module or shield on Arduino, Bleutooth on a PC connected to the wired network: 802.15.1 protocol, 1 MBPS (non EDR) speed, 10 meters range


Other options include IrDA, which has much greater data rates, but range of a couple of meters - Good for an RFI-heavy environment where the RF solutions fail. Then there are RF data modules such as the nrf24l01+ wireless transceiver that can be considered as well.

Without desired cost, data rate and range constraints, a more specific answer may be difficult to put together. 

I am refraining from suggesting smoke signals, Ouija boards, or a graduate student tasked with transcribing data into a data entry screen.