Check this link:
http://talk.sonymobi...om/thread/53822, see if your SI number is on the list. If the Xperia Sola's rollout of ICS is anything like my Xperia Mini's ICS rollout, Sony will do it in batches, so your phone might not be in the first batch. For my Xperia Mini it took about two months from the first batch to the last batch to get ICS, so you might have to wait a bit...
Anyway if your SI is there then connect your phone to the Sony PC Companion software to check for updates, the on-device "Update center" is (in my observation) usually delayed or does not work. I had been updating my Xperia Mini (including from Gingerbread to ICS) using PC Companion.