Bill, The TM-20 doesn't work with digital cell phones. Go to the pocketmail website
for more info (they do recommend a newer device, the PocketMail Composer
which is supposed to work with digital cell phones).
I've been using PocketMail for several years, and (alas) I have the TM-20 device... Even so, it's a great service. It really does work from almost any (land line) phone, although every once in awhile I hit a cranky pay phone that won't cooperate.
Of course, another drawback is it's just e-mail. No access to the www, which means no checking in on FiberglassRV.com. :nope