Jumping on a trend that’s becoming increasingly popular with U.S. ISPs, Shenandoah Telecommunications Co. has rolled out a pay-as-you-go Internet service.

That service, called Flex, offers 30 days of service for $19.99. Per the FAQ, vustomers are required to buy a $99 starter kit that comes with a wireless  modem, a month of service and a key card. Customers can refill by bringing the Flex Key Card to a ShenTel store or buy more access online flex.shentel.com (customers in the latter group must provide their modem’s MAC ID).

To keep the prepaid offering from cannibalizing its post-paid base, ShenTel limits Flex to  3 Mbps downstream. Customers who want or need more speed will need to take a post-paid service plan.

“Having in-home Internet access has become essential to everyday life. Flex is a great product for folks looking for an entry-level Internet service, without the burden of a contract and expensive monthly payments,” ShenTel vice president Tom Whitaker said, according to CED.

ShenTel joins other ISPs that are testing or have launched prepaid Internet offerings that are generally targeted to “unbanked” consumers, those with bad credit and others who do not otherwise qualify for a post-paid product.

Comcast started to test a prepaid Internet product in the fall of 2012, and has followed with a prepaid TV product in select areas that has recently begun to support HD as a baseline (the original prepaid TV product was standard-def only). Frontier Communications rolled out a prepaid Internet product more than a year ago.

Expanding on similar efforts underway in select markets in the northeastern U.S., Comcast has targeted a small set of stores in Florida as part of its ongoing trials of a prepaid Internet product.

Comcast is pitching the product, called Xfinity Internet Prepaid, at two BrandsMart stores in Miami, and another in Sunrise, a city in east-central Broward County. BrandsMart, a discount retailer, is also selling the Xfinity Internet Prepaid kit via its Web site.

Comcast has been selling its prepaid Internet offering at select retailers in parts of Philadelphia, New Jersey, Delaware, and Detroit, where it’s also testing a prepaid TV service.  Comcast has also set up a phone number (855-75-PREPAID) to accept and fulfill orders.

A Comcast official said the MSO’s prepaid products are still in the trial phase, and that the limited retail expansion in Florida is an effort to test out another small sample with different demographics.

Comcast began to trial prepaid Internet services in the fall of 2012, and limits it to consumers who do not have an active account with the MSO or otherwise do not qualify for one of its post-paid products.

For consumers who qualify, Comcast sells a prepaid Internet starter kit for $69.95 that comes with a DOCSIS 3.0 modem, required cabling and 30 days of service. After that, customers can obtain service refills -- $15 for seven days, or $45 for 30 days – by purchasing refill codes from participating retailers or online at a www.xfinityprepaid.net. Comcast limits the speed of its prepaid Internet product to 3 Mbps downstream by 768 kbps upstream.

Comcast, which ended the first quarter with about 21 million high-speed Internet subscribers, has not announced how many customers have taken its prepaid products, which are generally viewed as a low-risk option for lower income households and consumers who can’t qualify for post-paid services because they have poor credit or don’t have a bank account.