There's not nearly enough information in your post:
- what 'trouble'? 
- are you using the stock Messaging app? 
- is the problem with all of your contacts or only some? 
- what is your cellular signal like (how many bars)? 
- what firmware?
- if your contacts send you an SMS, do you receive it?
Sent from my rooted, debloated, deodexed Sinclair ZX-80 running CM 10.2 using Tapatalk 4