You can send free SMS to Bulgarian Operators if you have a registration at their sites. M-Tel, Vivacom and Globul are supported.
I know that some of you can`t see the contacts from the address book. This is because BG SMS Sender can only show your contacts from your google account. Contacts stored locally on the phone are not supported. I am working to enhance the contacts support.
Please send me feedback/bugs at vendor.net[at]gmail.com .