We have a small deployment of 7921g and 7925g phones. The 7925g phones while stationary when set to use the a band roam (while idle or in call) to distant APs with much weaker signal strength. That of course impacts negatively the quality of the call. The 7921 phones do not exhibit this behavior.
Access points and coverage:
Meraki MR14 & MR24 set to select their own channels (channel spreading) and auto reduce power according to the RF environment to avoid co-channel interference. Currently the APs transmit on channels 1, 6, 11 and 36, 44, 149 and 157.
Coverage has sufficient overlap for seamless roaming but it is really irrelevant in this case since the 7925 phones roam while stationary.
Initially 1.4.2 now the 7925s run 1.4.2ES.1
The phones have been configured to continuously update the AP list (CUCM setting) and channels on which the APs do not transmit have been excluded (through the web interface of the phones)
I have also noticed roaming issue with 7925G phones.
My phones have got configured scan mode for auto-RSSI, no power save.
When I use survey tool on the phones I can see all aps around with RSSI from -70 to -30dbm. The phone not always connects to the ap with the best noticed signal. When the call is placed the phones roam to the next ap randomly or when the ap drop the connection. Sometimes the phone handles connection to the ap with very low RSSI and reconnects to the nearest ap with the best signal only when is manualy kicked from the connected ap.
Other issue is that the all phones still uses power save mode even this mode is manualy disabled in the phones configuration ( I can see it in aps status) Phones leave power save mode only when the call is placed.
I would make sure you get the most recent code for the phones 1.4.3 SR1. I would also make sure you get a baseline and verify the wlc is setup correctly for a voice deployment. see the 7925 deployment guide below. I would also make sure you are not doing auto RSSI. If you havet he appropriate coverage for a, the set the phone for 802.11a and the voice wlan for A only also. I would also do a voice wireless site survey to make sure of the RF and also proper ap placement.