I just purchased a SMS data package from Verizon. I am able to send/receive SMS/MMS from any Verizon customers; however, not the same from AT&T, Sprint, and T-Mobile subscribers. Other non-Verizon subscribers report that they are able to receive my text message from my Galaxy tablet; however when then try to respond back, I am unable to receive those message. Is there a setting that I may have missed on my Tablet or is this a provider issue (e.g. firewall, VPN, et al)?