It’s not a rumor any more.
This was posted yesterday. Check here for the full post.
UNITED Micronesia Island Hopper Flight Number Changes from late-October 2013by JL
Update at 0615GMT 20JUL13
UNITED from 27OCT13 is adjusting operational flight numbers for its Micronesia Island Hopper service. Existing Eastbound service from Guam and Micronesian Islands to Honolulu, will switch from UA172 to UA155. Westbound flight from Honolulu and Micronesian Islands to Guam, remains unchanged.
So, if you are having trouble locating United flight 172, try looking for flight 155.
Then book a flight and come see us.