By David Russell, reporter at OptionMonsterNEW YORK -- Buyers tried to call the bottom in Vodafone ( VOD) for the second straight session Thursday. OptionMonster's trade scanners detected the purchase of 5,000 January 25 calls for 65 cents. That size was seven times greater than the strike's open interest at the beginning of the day, signaling fresh buying. Similar trades occurred on Wednesday, when the December 25 calls were purchased for 65 cents to 67 cents. Calls lock in the price where investors can buy the stock, making them highly leveraged to a rise in share price. For example, a gain of less than 5% will cause those contracts to appreciate by more than 50%. However, they will lose most or all of their value if the stock doesn't move. Vodafone shares fell 1.45% to $25.19 Thursday. The global telecom carrier has lost about 15% of its value in the last three months and now sits around the bottom of its trading range since late 2010. That could be leading some investors to think that it's ready to bounce. Calls outnumbered puts by almost 5 to 1 in the session. Russell has no positions in VOD.