Sprint appears to be the first US carrier to activate the Text 4 Syria campaign. By April 27th, all US carriers will be on board.
On Saturday April 25th, Sprint customers were finally able to donate using the Text 4 Syria campaign. A few testers texted "Syria" to 80077 and received a message to confirm that they want to contribute, and then confirmed the contribution. All worked flawlessly.
The other carriers are not fully functional yet, but by April 27th, all US mobile phone carriers should be active.
Stay tuned for more updates.