I formerly used a PO box, but I was paying for a PO box just for this. Then I used privacy, but GoDaddy are greedy. So now I use Tucows, and they give it for free. And as far as the pre-paid, you still have to top it up, or they'll cut it off.
PO Box costs me $50 per year, I use it as my main mailbox anyway since I don't trust my neighbors to not snoop.
The prepaid phone I have has two expirations. The first is based on minutes used- it counts down till its gone. It also keeps track of service days remaining, again counting down till its gone.
And its all too easy for one of these phones to end up with like 300 minutes and several years
of service time on it, making it ideal for a low cost point of contact to comply with ICANN regulations.
My domains are registered with dyn, and they want like $20 a year on top of the registration for the privacy service. Multiplied by the list of domains I have.
Using the PO box and prepaid phone instead, my info is compliant with ICANN regulations, but at the same time I am not inviting unwanted guests or getting a lot of telemarketters like I would be with a normal phone line and mailbox arrangement.