I don't think it is possible according to the [Apple dev spec](https://developer.apple.com/library/content/featuredarticles/iPhoneURLScheme_Reference/SMSLinks/SMSLinks.html) See also [StackOverflow](https://stackoverflow.com/questions/12818832/send-sms-to-mulitple-recipients)
No you probably right, I works with href="iMessage:email@example.com,firstname.lastname@example.org; but that is on the other hand on the computer if you want to send with iMessage on the mac. Thanks anyway Erik :-)
Well, this seams to work. href="sms:/open?addresses=0702315096,0707070707,0102315096,0207070707, 0302315096,0407070707,0502315096,0607070707,0802315096,0907070707,0712315096,0727070707,0732315096,0747070707,0752315096,0767070707,0772315096,0787070707,0792315096,0701070707,0703315096,0704070707,0705315096,0706070707,0707315096,0708070707,0709315096,0707170707,0702325096,0707870707," class="external" target="_blank">Send multiple imessage from iphone</a> :-) At least on an old iPhone 4S. I don´t have a new one to test with right now!?