Tracking cell phones and intercepting their calls are two very different things.
As a practical matter, intercepting cell phone calls does not require a warrant. Cell phones are two way radios and anyone can with the right equipment can listen in.
Try that in California and you might need Ted as a lawyer!
Iowa and other states probably have similar laws.
Chapter 1.5. Invasion of Privacy - California Penal Code Section 632.7
Laws > California Laws > Penal Code > Chapter 1.5. Invasion of Privacy - California Penal Code Section 632.7
632.7. (a) Every person who, without the consent of all parties to
a communication, intercepts or receives and intentionally records, or
assists in the interception or reception and intentional recordation
of, a communication transmitted between two cellular radio
telephones, a cellular radio telephone and a landline telephone, two
cordless telephones, a cordless telephone and a landline telephone,
or a cordless telephone and a cellular radio telephone, shall be
punished by a fine not exceeding two thousand five hundred dollars
($2,500), or by imprisonment in a county jail not exceeding one year,
or in the state prison, or by both that fine and imprisonment. If
the person has been convicted previously of a violation of this
section or of Section 631, 632, 632.5, 632.6, or 636, the person
shall be punished by a fine not exceeding ten thousand dollars
($10,000), by imprisonment in a county jail not exceeding one year,
or in the state prison, or by both that fine and imprisonment.
bad news indeed