Have you talked with Foca's support about it? You may need to cut a trace as the XBee S3B XSC uses different pins for some of the lines. Doing a quick comparison between the Boca schematic (http://store.iteadstudio.com/images/produce/Shield/Focav2.1/sch-foca-v2.1.pdf) and the XBee's product manual, (http://www.digi.com/support/productdetail?pid=5298&type=documentation) should allow you to verify that.