Before you buy a Sony Xperia U, Go, Sola and P do read my experience.
I recently bought a Sony Xperia U and when I arrived home I attached the sim card. It was weird coz the phone can't detect my contacts in the SUN sim card but it detects the globe sim card contacts. Reading sun sim card message, calling or texting works pretty well except for reading the sun sim contacts and transferring contacts from phone to sim. No issues with the Globe sim card. I even tried updating the firmware to the latest version.
So, the next day I brought the fone to the office and tested with 6 sun sim cards and all have the same issues. I asked my friend if this is also happening to his Xperia Ray and Xperia S and he responded that the sun sim card works pretty well.
I brought the phone to the Sony shop at ayala because I decided to change the phone to a higher model if ever the issue still exist with other Xperia U units. When I arrived, the technician immediately told me that the Sony Xperia U, Go, Sola and P are also experiencing the same issues. These series were having problems with older sun sim cards but not with Globe and Smart sim cards. He also told me that I wasn't the first customer to complain regarding that issue. Well of course sometimes we can't trust these folks coz maybe they are just trying to get rid of me. I then asked him if I could test the Sony Xperia Go to see if he wasn't lying.
He got a brand new Sony Xperia Go and we inserted the sim card and to no avail, he wasn't lying. The phone can't view my Sun Sim contacts. He told me that what he did with the previous customers was that he transferred the Sun sim contacts to an older sony android fone and bluetooth the contacts to the newer fone. And that the ICS update might solve the problem and also that the newer Sun sim cards won't have any issues with these series.
I decided to keep the Xperia U coz it is a really great decent phone and that my contacts are stored in the phone memory and synced with my google account. The only downside is that I can't read other older sun sim contacts. Better if they were android and their contacts were synced to their google contacts.