In places where the recipient pays (e.g. the US), you could upset some of your friends if you post too often to your photo sharing site, causing them to receive lots of SMS notifications.

In places where the sending party pays, then the service provider has to bear the cost directly, or pass it on to the end user. (This is presumably why Yahoo!’s free RSS-to-SMS service is only available in the US.)

IMS / SIP could potentially help solve this in future, with the possibility for a server to establish a direct connection to a mobile handset in order to push data to it.

On a related point, Cognima is building two-way data replication features into a future version of ShoZu. For example, when people visit your photostream on the
web and leave comments, you will be able to read the comment thread in the
ShoZu application on your phone. Comments are queued on the server and sent down to the phone whenever it connects (e.g. for a photo upload). The main benefit to users is that they can read comments on the move without having to
log in (via the phone browser) and check their account manually on
the off-chance that someone has left new comments (which, of course, often results in disappointment).

Not everyone has a Treo, though, and mobile blogging won’t take off unless the carriers and/or phone makers provide enough tools to help people post snapshots and text to the web in real time. We may see some very interesting apps in the next year or two, though.