[Sony Xperia P, U, Sola, Go] Sephirothrx7:
Here is a list of all available si codes for updating jb through pcc or sus.

1261-5829 LT22i/Mobile Phone/Proximus (Vfe) BE (Belgium)
1261-7022 LT22i/Mobile Phone/T-Mobile CZ (Czech republic)
1261-7024 LT22i/Mobile Phone/NT1-1/T-Mobile NL (Netherlands)
1262-0929 LT22i/Mobile Phone/Vipnet HR (Croatia)
1262-0962 LT22i/Mobile Phone/CA940/T-Mobile SK
1262-0965 LT22i/Mobile Phone/T-Mobile HR (Croatia)
1263-1947 LT22i/Mobile Phone/T-Mobile PL (Poland)
1263-2080 LT22i/Mobile Phone/NT1-1_IM820/Telstra AU (Australia)
1261-3348 LT22i/Mobile Phone/ET950_NT1-1_IM820/3 SE (Sweden)
1261-5237 LT22i/Mobile Phone/CA940_ET950/Customized TH (Thailand)
1261-5822 LT22i/Mobile Phone/ET950_IM820/Customized GBA (Greece and Balkan (b))
1261-5825 LT22i/Mobile Phone/ET950_IM820/Customized GR (Greece)
1261-5833 LT22i/Mobile Phone/NT1-1/Customized CH (Switzerland)
1261-5847 LT22i/Mobile Phone / Customized HK (Hong Kong)
1261-5851 LT22i/Mobile Phone / Customized TW (Taiwan)
1261-5853 LT22i/Mobile Phone / PT. Trikomsel OKE Tbk ID (Indonesia)
1261-5857 LT22i/Mobile Phone / PT. Surya Citra Multimedia (Indonesia)
1261-5987 LT22i/Mobile Phone/ET950_NT1-1_IM820/Customized PH (Philippines)
1261-5991 LT22i/Mobile Phone/CA940_IM820/GloBul BG (Bulgaria)
1261-7800 LT22i/Mobile Phone / CJ / Customized AU (Australia)
1261-7821 LT22i/Mobile Phone/CA940_NT1-1/Customized IN (India)
1261-7827 LT22i/Mobile Phone/ET950_NT1-1_IM820/Customized IT (Italy)
1261-8045 LT22i/Mobile Phone/ET950_NT1-1_IM820/O2 Pay monthly UK (United Kingdom)
1261-8163 LT22i/Mobile Phone/ET950_IM820/Customized ZA (South Africa)
1261-8227 LT22i/Mobile Phone/IM820/MOBITEL SI (Slovenia)
1261-8235 LT22i/Mobile Phone / T-Mobile HU (Hungary)
1261-8592 LT22i/Mobile Phone/CA940_ET950_NT1-1_IM820/Customized CE1 (Central Europe 1)
1261-8955 LT22i/Mobile Phone/NT1-1_IM820/SingTel SG (Singapore)
1261-9011 LT22i/Mobile Phone/ET950_NT1-1_IM820/Customized TR (Turkey)
1262-0876 LT22i/Mobile Phone/AN400/EC480/Customized MY (Malaysia)
1262-1442 LT22i/Mobile Phone/ET950_NT1-1_IM820/Customized RU (Russia)
1262-1484 LT22i/Mobile Phone/NT1-1/Customized DE (Germany)
1262-3237 LT22i/Mobile Phone / MobilTel EAD BG (Bulgaria)
1262-3489 LT22i/Mobile Phone/IM820/Vodafone HU (Hungary)
1262-3522 LT22i/Mobile Phone/NT1-1_NT1-2_IM820/Vodafone NZ (New Zealand)
1262-3584 LT22i/Mobile Phone/ET950_NT1-1_IM820/Telenor DK (Denmark)
1262-3586 LT22i/Mobile Phone/ET950_NT1-1_IM820/Telia DK (Denmark)
1262-3618 LT22i/Mobile Phone/ET950_NT1-1_IM820/TDC Mobil DK (Denmark)
1262-3688 LT22i/Mobile Phone/ET950_NT1-1_IM820/Customized BAL (Baltic Generic (b))
1262-4729 LT22i/Mobile Phone / China Unicom CN (China)
1262-7436 LT22i/Mobile Phone/NT1-1/o2 DE (Germany)
1262-8812 LT22i/Mobile Phone/ET950_NT1-1_IM820/Customized UA (Ukraine)
1264-3189 LT22i/Mobile Phone / Customized US (USA)
1265-2714 LT22i/Mobile Phone / Customized BE (Belgium)
1266-7817 LT22i/Mobile Phone/CA940_ET950/Customized_i IL (Israel)
1261-8942 LT22i/Mobile Phone/ET950_NT1-1_IM820/Yoigo ES (Spain)
1261-9622 LT22i/Mobile Phone/Customized CN (China)
1262-3681 LT22i/Mobile Phone/ET950_NT1-1_IM820/Customized NC (Nordic Combined (b)
1262-0972 LT22i/Mobile Phone/ET950_NT1-1/Customized FR (France)
1262-1412 LT22i/Mobile Phone/NT1-1/3 AT (Austria)

*Updated list with region and network operator, courtesy of sijav*

SI's for new JB update

1261-5237
1261-5829
1261-5833
1261-5841
1261-5843
1261-5847
1261-5851
1261-5853
1261-5857
1261-5987
1261-5991
1261-6006
1261-7009
1261-7022
1261-7024
1261-7800
1261-7815
1261-7821
1261-8045
1261-8075
1261-8227
1261-8229
1261-8258
1261-8592
1261-8609
1261-8955
1261-9133
1262-0802
1262-0821
1262-0876
1262-0929
1262-0932
1262-0962
1262-0965
1262-0972
1262-1412
1262-1484
1262-3254
1262-3484
1262-3489
1262-3503
1262-3681
1262-5104
1262-5106
1262-7436
1262-8812
1263-1947
1263-4831
1265-2714
1266-7817

To change si code, you need to edit build.prop. Set the following lines to the choosen SI code (remeber to only change the 8 si numbers):

ro.product.name=LT22i_1261-8592
ro.semc.version.cust=1261-8592

Just change the numbers to the si code you want to use.

and ro.semc.version.cust_revision to R1G, just to be sure

ro.semc.version.cust_revision=R1G

You need root for this. After that, reboot phone and check on sus or pcc. If you update, please provide a ftf so other users can try too.

SI codes are regional/customization codes, you can check what brand/region is the code by searching on the attachment file. For example, 1264-3189 is the generic US firmware.

One notice: I cannot guarantee that these SI codes will work on devices other than xperia p, as I have extracted them from the firmware list for xperia P attached on the post.