Parents who fear giving their teens or younger children a "credit card with an antenna" are getting some help from carriers who are introducing services that help parents control their child's cellphone use. The NYT has a detailed story on the various plans available, including T-Mobile's new "Family Allowances," plan launched today, similar to AT&T's "Smart Limits" offering. Verizon ( NYSE: VZ), too, has one in the works, leaving Sprint ( NYSE: S) as the only major carrier without one. For a monthly fee, the services allow parents to cap the number of minutes and text messages, block certain phone numbers, and even limit the time of day when the phone can call out. T-Mobile's plan has an introductory price of $2 a month, while AT&T's cost $5. But the NYT points out that AT&T's has more features, and more flexibility.