Numbers with this prefix were first introduced in 2004.While 2154100987 was originally issued with the info above, the owner of the phone number (215) 410-0987 may have transferred it through a process called porting.
Caller type: Text/SMS
Seems like spam or a virus. According to this site, other numbers have reported the same message verbatim. It says:
You've been selected to win a FREE Walmart Giftcard worth $1000! Enter the code 'FREE' at www.walmart.com.whmt.biz to get 1 now! Only 188 left. Text STP to stop