Some years ago I looked into prepaid pricing and determined that it was significantly more expensive than a subscription plan at even my almost-never-use-it levels of phone use. (At that time, pricing was based on (1) a reasonable per-use rate, which would have been very cheap; combined with (2) a high flat fee charged on any day you used any feature of the plan, which already nullified any price advantage; and (3) a requirement to add funding to the plan every month, regardless of whether you had an existing balance.)
How they work here is:
1. You need to top up by €20 at least once a year to keep your account
2. You may sign up to an offer, which will deduct a portion of a top up each month to activate the offer (e.g top up by > €20, the phone company takes €10 for unlimited texts, or €20 for unlimited data).
3. If you don't top up as required by your offer, you fall back to a state as if you had no offer
4. If you have no offer there's fixed fees of like 20c/sms and €0.50/min of calls, €2/day for 100mb of data
Now pre-paid is often just paying for a month before usage rather than after usage. Even cheaper providers like Mint sign you up for 3 months at once, which can get expensive if all you want it for is just satisfying Twitter.
Is it reasonable for everybody to go buy "burner" phones to sign up for Twitter?
The truth is, it's stupid for Twitter to require a phone number, and it's especially stupid that they blame the user for using their real number.