Require sms confirmation to create account
When users add their mobile phone number, a confirmation code is sent out. Is there any way to disable the user's account completely until they have entered this confirmation code? Or perhaps to move them to a new role when they have confirmed their mobile phone number? I want to only allow users from the UK to create accounts, and requiring them to enter a UK phone number seems a good way of achieving that.
Perhaps you have some other suggestions on how this might be achieved?

In function
In function sms_user_settings_confirm_form_submit you can add the following code after the user_save function is called. It seems to add the user to role 6. Obviously it would be nice to get this coded nicely with the relevant forms for settings, but it works for me.
<?php$rid = 6;
$role_name = db_result(db_query('SELECT name FROM {role} WHERE rid = %d', $rid));
if ($account !== FALSE && !isset($account->roles[$rid])) {
$roles = $account->roles + array($rid => $role_name);
user_save($account, array('roles' => $roles));
}
?>
IP based location?
http://groups.drupal.org/node/15312 lists some modules that lookup countries based on IP address. That could be another way to implement your requirement.
Russell JVM Gutierrez
Manager, Hong Kong Projects
flippingNORMALS
Web | Social Media | Mobile
Not enough
We've considered using IP based location, but that's problematic. It doesn't always guess the country correctly, and it wouldn't discourage people from creating duplicate accounts in the same way that having to send an sms message from a unique phone number would.
I've seen an upcoming social network use Facebook as their one and only authentication method, because people don't lie on their facebook accounts. The idea is nice, but forcing people to have a Facebook account really really sucks.
Another option, which we
Another option, which we have settled on, is to ditch sms_framework entirely and just use a small php script which receives messages from txtlocal and enters new email addresses sent by uk telephone numbers into a csv file. The User_import module, with a small amount of customisation, will then import new entries in that csv file every hour or so using cron.