I recently drove to DC and back playing dances in a rental. I paid cash tolls when available, but that often wasn't an option, so I ended up paying $40 in PlatePass charges in addition to the $63 in tolls. Time to get an E-ZPass!
What makes this tricky is that I don't own a car. Well, I have half a car, which does have an E-ZPass, but that stays with that car. If you go to sign up online you'll get through to step 5 of 7 and then:
Please add at least one vehicle to your account. If you do not have a vehicle please call the customer service center to open your account. You may not request more transponders than you have vehicles on your account.
Then you call customer service, and when you follow the prompts to tell the automated system that you want to open an E-ZPass account they tell you this must be done online and don't offer any other options.
If you do get through to a person, for example by pressing 2-2-9 to tell them that you have a question about your account but have forgotten your number, they'll tell you to go online to their Document Library, fill out a PDF application, and fax it in. The only difference, as far as I can tell, is that the PDF form isn't capable of complaining when you don't enter a license plate number.
Which worked! Now I have a transponder, and when I want to rent a car I can follow their instructions to add it to my account as a short-term rental.
Note that you don't have to be an MA resident to get an MA E-ZPass [1]. Several states have fees or inactivity charges, but MA is one of the ones that doesn't. If you drive a lot you'll often make up for the fees by lower in-state tolls, but if you don't then it could be worth getting a fee-free one from MA or another no-fee state.
[1] This is actually a requirement for offering discounts on MA
highways to MA EZ-Pass accounts; see Yerger
et al. v. Massachusetts Turnpike Authority:
We agree with the District Court. The FLDP does not use E-ZPass as a proxy for Massachusetts citizenship to achieve discrimination despite a facially neutral program; rather, it offers all Fast Lane enrollees, regardless of citizenship, access to toll discounts on the same terms. The fact that more Massachusetts citizens than out-of-state citizens may work in the Boston area, and therefore have a greater incentive to join Fast Lane, does not demonstrate that the program is unconstitutionally discriminatory.