Involved in BCR (B-cell antigen receptor)-mediated signaling in B-cells. May also be involved in FCER1 (high affinity immunoglobulin epsilon receptor)-mediated signaling in mast cells and FCGR1 (high affinity immunoglobulin gamma Fc receptor I)-mediated signaling in myeloid cells. Couples activation of these receptors and their associated kinases with distal intracellular events such as calcium mobilization through the recruitment of GRB2. When phosphorylated, interacts with GRB2. Present in lipid rafts. Phosphorylated on tyrosines following cross-linking of BCR; which induces the recruitment of GRB2.