Why an attacker should spend 100$ , sending hardware to the target that could be potentially tracked following the path between the resellers, could transport evidences like fingerprints or DNA, using a telephone connection that could also be tracked when the same thing could be done with a good radio equipment and more discretion ? Anyway, I am the kind of guy that inspects the ATM praying to find out a skimmer to dissect, so if someone would send me all that cool stuff directly at home is welcome !
Moreover: battery. How many time a battery of reasonable dimensions could survive powering that kind of system ? exaggerating, 3 days without using a heavy use of the phone modem ? But let's say that in that time the attacker reach the target collecting WIFI keys that doesn't mean that he can compromise any PC or phone in the home network. So my advise is to send directly networking hardware compromised (i.e. an access point ) and, if your budget is 100$ , you can send a very nice piece of hardware to the target, avoiding that he throws all that stuff away (if he can't recycle all like me ). Again, if someone could send me a free, 100$ worth AP is welcome.