How to Lift 10 SMS Recipients Limit on HTC Sense
If you are texting alot and you are used to sending multiple recipient text messages, you might have noticed that the Compose screen is by default limiting you in sending a text message to maximum 10 recipients.
If you find this annoying, you can easily lift that limit via editing your Registry; go to HKLMSoftwareJataayuMessaging and edit the value of MaxRecipients from the default 10 to a number of your choice (I’ve raised it to 30). Soft reset your device and you’ve lifted your SMS recipient limit.
(Source: XDA Developers)