Some offer the conjecture that such treatment of customer will in some way hurt the company. I doubt that is the case. The percentage of their users using Asterisk to pass calls to them is likely extremely small. It’s also quite likely very obvious to them, both in terms of average minutes per user per month and the reported SIP client name.
I simply can’t beleive how many people go to such trouble to take advantage of Magic Jack as an Asterisk trunk when it clearly violates the TOS. Minutes through legitimate means are dirt cheap so why bother with such a hack.
OTOH, just as people have used HP thin clients to host the Magic Jack dongle, someone could in theory put together a hardware hack that would turn a legitimate MJ dongle in a T57xx into an ATA-like gateway device. It would need to take the call into the MJ dongle, but redirect the audio streams to another process, passing back onto the network to reach the Asterisk server as a SIP connection. A strange kind of back-to-back-user-agent (B2BUA.)
This would be a curious hack. Of course anyone could plug an RJ-11 line into the MJ dongle and bring it into an FXO on the PBX. Avoiding the use of an FXO interface on the Asterisk box would improve call quality, and keep the cost down. Since MJ users seem cost sensitive I presume that would be a consideration.