如何将信息从一个站点合并到另一个站点？

Lets say I have two sites www.a.com and www.b.com. There is a newsletter subscription form on site www.a.com and i need to incorporate that submitted information to site www.b.com and information will be name, address,newsletter format and email id of the subscriber. Is there any way to do so. I am using PHP. Lets say I have two sites www.a.com and www.b.c