Looks like thick coax (RG-11 or similar). Outer black sheath, inner foam core, probably some foil or mesh shielding sandwiched between the layers, and I think I can barely make out the inner conductor.
If that's what it is, it's not likely for your U-verse or Verizon service. 9 times out of 10 U-verse is delivered over twisted pair (VDSL) and I'm assuming your Verizon service is regular POTS (also twisted pair). If FIOS, then you'll have fiber to a transceiver box on your house. This is likely left over from old cable service to your house.