Some phones sold by Straight Talk use the Verizon network, and some do not. Each phone the company sells is assigned to its own home network. The brand also features phones that use T-mobile, AT&T, Sprint and regional carriers to provide call and data services.
When buying a new phone, one easy way to determine whether or not it uses the Verizon network is to read the CDMA code. This code is generally found on the front of the phone's box in the lower left corner. Verizon phones will be denoted with a code of "cdma-V." Non-Smartphones with model numbers ending with the letter C always use Verizon towers.