[HTC Sensation] zswielder:
Build.prop file is under Systems folder. When I was on AT&T with HTC Inspire, we could modify values in it to get higher speeds. Here are some info I found about different values/categories in build.prop.

Found this on XDA:

There are many ro.ril parameters which I found from /system/lib/libhtc_ril.so:

ro.ril.a52.%s (gprs encryption algorithm)

ro.ril.a53.%s (gprs encryption algorithm)

ro.ril.ecc.%s (emergency call codes)

ro.ril.def.agps.mode.%s (network assisted gps)

ro.ril.def.agps.feature.%s (network assisted gps)

ro.ril.def.agps.mode (network assisted gps)

ro.ril.def.agps.feature (network assisted gps)

ro.ril.oem.ecclist (emergency call codes)

ro.ril.oem.nosim.ecclist (emergency call codes)

ro.ril.gprsclass (http://www.cellular-...g_schemes.shtml)

ro.ril.hsdpa.category

Spoiler

#ro.ril.hsdpa.category :

# Cat 1 = 1.2 Mbit/s

# Cat 2 = 1.2 Mbit/s

# Cat 3 = 1.8 Mbit/s

# Cat 4 = 1.8 Mbit/s

# Cat 5 = 3.6 Mbit/s

# Cat 6 = 3.6 Mbit/s

# Cat 7 = 7.2 Mbit/s

# Cat 8 = 7.2 Mbit/s

# Cat 9 = 10.1 Mbit/s

# Cat 10 = 14.0 Mbit/s

# Cat 11 = 0.9 Mbit/s

# Cat 12 = 1.8 Mbit/s

# Cat 13 = 17.6 Mbit/s

# Cat 14 = 21.1 Mbit/s

# Cat 15 = 23.4 Mbit/s

# Cat 16 = 27.9 Mbit/s

# Cat 19 = 35.3 Mbit/s

# Cat 20 = 42.2 Mbit/s

# Cat 21 = 23.4 Mbit/s

# Cat 22 = 27.9 Mbit/s

# Cat 23 = 35.3 Mbit/s

# Cat 24 = 42.2 Mbit/s

# Cat 25 = 46.8 Mbit/s

# Cat 26 = 55.9 Mbit/s

# Cat 27 = 70.6 Mbit/s

# Cat 28 = 84.4 Mbit/s

ro.ril.hsupa.category

Spoiler

#ro.ril.hsupa.category :

# Cat 1 = 0.73 Mbit/s

# Cat 2 = 1.46 Mbit/s

# Cat 3 = 1.46 Mbit/s

# Cat 4 = 2.93 Mbit/s

# Cat 5 = 2.00 Mbit/s

# Cat 6 = 5.76 Mbit/s

# Cat 7 = 11.5 Mbit/s

ro.ril.hsxpa:

ro.ril.hsxpa=0 – UMTS r99

ro.ril.hsxpa=1 – HSDPA

ro.ril.hsxpa=2 – HSDPA/HSUPA

ro.ril.enable.nitz (network informed time zone)

ro.ril.enable.network_identify

ro.ril.enable.dtm (Dual Transfer Mode)(ro.ril.enable.dtm : Only set this to 1 if your network allows simultaneous transfer of Circuit switched (CS) voice and Packet switched (PS) data over the same radio channel (ARFCN).

qos (quality of service)

ro.ril.qos.maxpdps

ro.ril.qos.traffic.class

ro.ril.qos.max.ul

ro.ril.qos.max.dl

ro.ril.qos.guarantee.ul

ro.ril.qos.guarantee.dl

ro.ril.qos.delivery.order

ro.ril.qos.max.sdu

ro.ril.qos.delivery.err.sdu

ro.ril.qos.transfer.delay

ro.ril.qos.traffic.priority

ro.ril.always.laccid

ro.ril.fast.dormancy.rule

ro.ril.fd.scron.timeout

ro.ril.fd.scroff.timeout

ro.ril.fast.dormancy.plmn

ro.ril.enable.3g.prefix (=1 shows "3g" on lock screen next to network name, =0 does not)

ro.ril.3g.long.name

ro.ril.htcmaskw1.bitmask

ro.ril.htcmaskw1

ro.ril.enable.homezone

ro.ril.enable.vt

ro.ril.enable.regucid

ro.ril.enable.hsdpaind (perhaps ind stands for indicator?)

ro.ril.enable.a52

ro.ril.enable.a53

ro.ril.enable.dcm.feature

ro.ril.enhance.htcdis

ro.ril.enable.tim.feature

ro.ril.enable.korea.stk (Korean Sim Tool Kit)

ro.ril.enable.hsupaind (perhaps ind stands for indicator?)

ro.ril.enable.gea3 (gsm security algorithm)

ro.ril.enable.managed.roaming

ro.ril.enable.enhance.search

ro.ril.disable.mcc.filter

ro.ril.search.first.pnn

ro.ril.enable.ncell.ind (neighboring cell)

ro.ril.enable.enhance.nws

ro.ril.radio.svn

ro.ril.wp.feature

ro.ril.emc.mode

ro.ril.ucsq.mode

ro.ril.disable.power.collapse (said to be an ultra-low power state when phone is in idle, saving battery) (so does =1 mean "yes, please disable the power collapse mode", and =0 mean "oh, please leave power collapse mode on")

ro.ril.enable.cnap (Caller Name Presentation)