How likely is it that my friend will have to serve the rest of his original sentence?

If your friend violated probation by using the internet to access child pornography and associating with other known sex offenders, he likely could serve a significant portion of it plus a new sentence. Depending on the factual circumstances of the violation probation, he may not serve the entire amount because the state is likely to want to hang some of the remainder to continue his probation for a while longer. If he served the entire amount of the suspended sentence, the probation would terminate. However, with the new bond being $150,000 on possession of child porn by a convicted sex offender, it is likely the new charges are very serious and the violation of probation may be the least of his worries. If the violation can be served concurrently with any new sentence, he may want to consider that.