As you pointed out SMS is a very important channel for viral invites, in fact, we at GetSocial.im have seen SMS to be the second most popular channel (after WhatsApp) in driving virality. Recently we did a study together with Sega Hardlight which you can see here.
Average click to Install conversion for SMS we have seen is around 25%, whereas sent to install conversion is around 5%. SMS as an invite channel is more successful in US where we see twice the conversion.
Viral Patel (Founder @ GetSocial)