Slow when connected via Iptouch 4018

[prabhath]

Guys,
this iz ittle bit strange issue and need ur help.

I have one OmniStack LS 6248P in data vlan15 and voice vlan 10.And users connected via Alcatel iptouch 4018 desk phones.Sine 2 weeks time users are not able send email or acces internet fast. It's really really slow. But I have another switch with same vlan no issues at all.
Other thing is if i connect users directly to network port or switch port without phone everything works fine. Switch running-config is attached.
Application software identity=R10.0-j1.410-40-c-ae-c82
Business identification: R10.0
And conputer lan speed i ican see 100mbps. as a example if i need to send email it stays 4-5 minutes in outbox.we use exchange email which server it lying in site to site vlan site.in sonicwall firewall we don't get any packets from this switch users.
Any kind of help is really appreciated.

[prabhath]

Software Version 1.7.1.7
Boot Version 1.0.0.13