I went trough the English language strings in GoSMS to find anything that resembles an invitation message. If a messaged popped up containing text, it had to be saved somewhere. See below for strings related to "invite".

Code:
Select Code
    <string name="goim_invite_message">Send SMS to invite him/her to use GO Chat, so that you can chat freely?</string>
    <string name="goim_invite_title">Invitation</string>
    <string name="goim_invite_send">Send</string>
    <string name="goim_invite_confirm_mesage">Invite he/she to verify phone number, improve personal material?</string>
    <string name="goim_invite_confirm_sms">Hi, Please bind your mobile number with GO Chat (Menu-> My profile), which will improve your GO Chat experience</string>
    <string name="contact_invite">GOChat invite</string>
    <string name="contact_invite_verify">Verify number</string>
    <string name="invite_people_to_use_goim">Now invite friends to use GO Chat, send online free messages.</string>
    <string name="gotips_content">Recommend you to send an SMS to invite him/her to use GO Chat, which opens up the channel to send message for free.</string>
    <string name="gouser_click_tips">Recommend him/her to use GO Chat? Click here to invite him/her to be your GO Chat friend and send message for free.</string>
    <string name="gochat_invite_message">Send SMS to invite him/her to use GO Chat so that you can chat for free?</string>
    <string name="send_invite_msg">The invitation has been sent</string>
    <string name="goim_login_invite_msg">Your GO Chat is logout. Do you want to login and send an SMS to invite him/her to be your GO Chat friend?</string>
    <string name="goim_new_invite_sms">Invite U to be my GO Chat friend%s Download: 61.145.124.93/soft/gosms/GOSmsPro.apk</string>
    <string name="invite_success">Invite succeeded.</string>
    <string name="invite_failed">Invite failed.</string>
    <string name="invite_none">They have joined the group, will not be invited again.</string>
    <string name="someone_invite_you">%1$s invite you%2$s into the room</string>
    <string name="you_invite_someone">you invite %1$s into the room</string>
    <string name="someone_invite_others">%1$s invite %2$s into the room</string>
    <string name="invite_now">Invite</string>
I also investigated the possibility, that GoSMS could be able to read the recipient of incoming messages, which would be the phone number. However GoSMS doesn't do the actual receiving but rather lets Android do the work and reads messages from a framework call. Since Android doesn't save the the recipients I'd say this is a dead end as well.

Again, feel free to double check everything.