One type of spam that I've been spared so far is SMS spam, where spam messages are sent directly to your cellphone (often very expensive for the recipient). Stock spammers in the US often use SMS spam, while in places like China it's already a huge problem. In Britain, two-thirds of cellphone users have received SMS spam.

If you're getting SMS spam, you're really at the mercy of your cellphone provider. Filtering 'on the phone' doesn't make a lot of sense, especially if your cellphone plan charges you for incoming messages. The tendency of spam is always to increase, so SMS spam is very bad news for users who pay per message: when the spams starts flooding in, it will either bankrupt you or it will wipe out your allowance for the month.

So it's good to learn in this article about SMS spam by David Pogue that there are things you can do, at least if you live in the US. It turns out that most of the major providers offer some kind of blocking feature, and the article explains how you can take advantage of these. If you live outside the US, or your provider isn't mentioned in the article, it's worth calling to find out what you can do.

The not-so-good news is that blocking features implemented by different providers seem somewhat haphazard and, as usual, blocking spam comes at the cost of forgoing some useful features. For example, most providers offer you the possibility of blocking SMS messages that originated from the Internet rather than a cellphone, immediately protecting you from a large amount of SMS spam. The problem is that a blanket block also shuts out messages you might want, such as messages from Twitter or a flight tracking service - or, if you're a system administrator, pages from failing hardware.

Cellphone providers have a mixed incentive to block SMS spam. If they're charging per message, then they don't really care if the messages that you get are good or bad. The risk that customers will vote with their feet and move to another carrier is reduced by the fact that customers are typically on a fixed-term plan specifically designed to tie them in and limit their freedom of movement. A provider could, in theory, choose to ignore the SMS spam problem or to see it not as a menace but as a profit center.

Realistically, a carrier that does this is going to hurt its long-term business fairly severely, especially if the SMS problem grows — and it will, if measures aren't taken to stop it. So what can carriers do?

A first step would be to allow customers to block messages originating from designated 'zones', such as the Internet, or overseas, or other cell networks (as one source is blocked off, spammers will find another). However, blanket blocks shut out useful features as well, so cellphone users need to be able to whitelist known good sources as well. A mass-block-and-whitelist approach is the only one that really makes sense — trying to blacklist a constantly changing array of spam sources is a game of whack-a-mole that neither providers nor customers want to play.

For whitelisting to work, the provider needs to be sure that a message really originates where it says it does. Whitelisting on the 'From' line of an email is an obviously bad idea — unless you can use something like SPF to verify that it comes from an allowed sender with a restrictive SPF policy. This also means that the would-be sender must communicate clearly to the user exactly what they need to add to their whitelist in order for the message to be accepted.

None of this will make cellphone users' lives easier. Properly protecting cellphones against spam is not something that lends itself to push-button simplicity. Nevertheless, block-and-whitelist approaches make some sense in the world of SMS messaging where users don't generally expect to receive text messages from total strangers. Similar approaches are less applicable to the promiscuous world of email, where, historically at least, the expectation has been that desirable email might come from anywhere at any time, making blanket blocking inappropriate.