Sales calls. Here is their corporate information:

Vitelity, Llc.
XO Communications - Syniverse
Most likely a google voice number since people with Google have Synierse as the real carrrier

Corporate Headquarters
7900 E Union Ave.
Suite 1100
Denver, CO 80237
Phone: (888) 898-4835
FAX: (303) 991-7999

http://www.vitelity.com/headquarters

Someone calls me once a week from this number and I have no idea who it is and why they keep calling without leaving a message.

hello who is this number belongs to, jus mentio ur initial is the safe way.