For pre-paid the cheapest is $15 for 365 days.
I couldn't believe that I didn't know about that plan (since one of my 'hobbies' is trying to get the cheapest phone service possible), but then I saw it was for Australia - what a let down.
That said, here's my wall-of-text on cheap paygo in the US:
Many pay-as-you-go (paygo) plans are very inexpensive for low use, but they all have some expiration date on unused funds and/or require you to pay some amount very few months to keep the phone service active. All of the following information is for the US (and for US to US calls). I'll also not be discussing data - voice and text only.
I'd suggest getting an unlocked GSM phone since that makes it *very* easy to select or change plans. It's pretty easy to find an unlocked feature phone for less than $20. If you want an Android phone it'll be a little more difficult, but some very low-end ones can be found in the $30-40 range that are either unlocked or easy & cheap to get an unlocked on eBay or a third-party unlock site (this is completely legal). For voice & text, pretty much any GSM phone today will have the frequency support for any GSM provider, so all you have to worry about with a GSM phone (for voice/text) is that it is unlocked and you'll be able to use it.
There are two main GSM providers in the US (T-Mobile and AT&T); most of the 'off-brand' paygo providers are actually reselling service from one of these carriers. AT&T has better coverage than T-Mobile. Verizon has even better coverage than AT&T, but isn't a GSM carrier, so I won't consider them in the remainder of this post. Depending on where you live, the coverage might matter in your selection of a plan.
A couple of websites that have a lot of information on these phones and plans:
Some plans that I'm aware of:
- T-Mobile paygo: 10 min/10 text - there is a minimum $3.00 per month charge
- H20 paygo: 5 min/5 text - must add at least $10 every 3 months
- PTel: 5 min/2 text - must add at least $10 every 2 months
- Truphone: 9 min/9 text - (Note: I have not used Truphone myself) Truphone used to offer non-expiring funds. Today I can't find any information about their fund expiration policies. If you check with their customer service and their policy is still to never expire funds and keep the phone active, then this might be a great plan to go with. I might have to look into this for myself again...
- LycaMobile: 2 min/ 4 text - Lyca used to allow you to carry your funds for an unlimited amount of time as long as you made at least one call or text in a 3 month period. They have changed things around several months ago and it's not clear to me if that policy is still in effect. Their website doesn't even mention paygo anymore, but reports are that it is still offered. Lyca was (and still might be) a great plan for low-use phones, but the web site is terrible and the customer service isn't really any better. I used Lyca for quite a while; when it worked it was a tremendous value, but then some things stopped working for me (Google voice integration being the main one), and I couldn't get any help. That plus the lack of clarity on new policies made me decide to move away. However, I'm considering moving back since it seems like people aren't having their funds expire in practice and I think a new SIM will possibly solve my GV problem.
I'd say that for the least hassle, get a T-Mobile paygo plan and drop $40 onto it - you'll get a year+ of service, but Truphone might be worth a look.