One of a million problem on IOS 7 is fail to sending text message. User (especially who using rsim, gevey or gpp) can't use text message anymore. Maybe they think that everyone use i message now, that is suck.
This is a working solution for you who face problem with text message. So simple, but you have to re-write your contact. Let me know if you have another simple working solution. First, please make sure, that your device allowed text message. (Setting-message-turn on send as SMS)
Step by step for text message problem on I.O.S 7 (working until IOS 7.0.4)
1. Remember your contact number, write on note or paper, then delete it (contact-edit-scroll down-delete)
2. Compose new message, write manually the phone number without country number, use '0'