These scoundrels call from a variety of numbers. I don't know what percentage of those numbers are spoofed Caller ID, though. here's one: http://800notes.com/Phone.aspx/1-844-336-6283
Something called the Purple Heart Foundation certainly exists - they have a web site at www.purpleheartfoundation.org.
Charity Navigator has no record of them at all, either as "Purple Heart Foundation"
(http://www.charitynavigator.org/index.cfm?bay=search.alpha&ltr=P ) or the name which appears on the web site, "Military Order of the Purple Heart Service Foundation, Inc." (http://www.charitynavigator.org/index.cfm?bay=search.alpha&ltr=M ).
"Military Order of the Purple Heart Service Foundation, Inc.", however, *is* listed on the IRS web site of organizations eligible for tax deductible contributions, so they would seem to be legal. Their EIN is 39-0983584 and they're based in Annandale, VA. See http://www.irs.gov/Charities-&-Non-Profits/Exempt-Organizations-Select-Check
Still, the fact that Charity navigator has no record of them is a big red flag as far as I'm concerned.
Chances are they've made the (foolish) decision to do telephone solicitations for donations and these calls are almost certainly coming from a call center that makes calls for multiple charities and other clients. Typically, these call centers take a large part of each donation and only a small amount goes to the actual charity (though of course I have no information on this specific case). Anyone truly wanting to help the charity in question is much better off writing a check to the organization or donating directly through the charity's own web site, so that *all* your donation really goes to the charity. Don't EVER give your credit card number or bank information to ANYONE who calls on the phone, charity or otherwise!
If the caller tries to talk you out of making a direct donation to the charity and pressures you to donate right now by phone you can be fairly certain you're dealing with a third-party call center who keeps most of the money for themselves.