modem-manager prevented suspend

My laptop failed to suspend and returned to a locked screen. After unlocking and re-attempting to suspend, the same problem occurred. Below is the relevant part of the dmesg. Notice how "modem-manager" fails to freeze:

[78092.127297] PM: Syncing filesystems ... done.
[78092.136916] PM: Preparing system for mem sleep
[78092.137002] Freezing user space processes ...
[78112.150201] Freezing of tasks failed after 20.01 seconds (1 tasks refusing to freeze):
[78112.150431] modem-manager D 000000010072c2de 0 21071 1 0x00800004
[78112.150679] ffff880053b25b08 0000000000000082 0000000000000000 0000000000015b80
[78112.151074] ffff880053b25fd8 0000000000015b80 ffff880053b25fd8 ffff880074a42de0
[78112.151470] 0000000000015b80 0000000000015b80 ffff880053b25fd8 0000000000015b80
[78112.151862] Call Trace:
[78112.151953] [<ffffffff8158c457>] __mutex_lock_slowpath+0xf7/0x180
[78112.152047] [<ffffffff8158c33b>] mutex_lock+0x2b/0x50
[78112.152139] [<ffffffffa0c067a8>] acm_tty_open+0x28/0x2e0 [cdc_acm]
[78112.152236] [<ffffffff81359aca>] tty_open+0x20a/0x610
[78112.152329] [<ffffffff81158a9a>] chrdev_open+0x10a/0x200
[78112.152421] [<ffffffff81158990>] ? chrdev_open+0x0/0x200
[78112.152523] [<ffffffff81152ef5>] __dentry_open+0xe5/0x330
[78112.152631] [<ffffffff81262eaf>] ? security_inode_permission+0x1f/0x30
[78112.152727] [<ffffffff81153254>] nameidata_to_filp+0x54/0x70
[78112.152820] [<ffffffff8115ffd8>] finish_open+0xe8/0x1d0
[78112.152912] [<ffffffff81168c5f>] ? dput+0xdf/0x1b0
[78112.153002] [<ffffffff81161436>] do_last+0x86/0x460
[78112.153114] [<ffffffff8116376b>] do_filp_open+0x21b/0x660
[78112.153228] [<ffffffff81103397>] ? unlock_page+0x27/0x30
[78112.153342] [<ffffffff81123499>] ? handle_mm_fault+0x1b9/0x440
[78112.153448] [<ffffffff8116ef9a>] ? alloc_fd+0x10a/0x150
[78112.153561] [<ffffffff81152c99>] do_sys_open+0x69/0x170
[78112.153673] [<ffffffff81152de0>] sys_open+0x20/0x30
[78112.153787] [<ffffffff8100a0f2>] system_call_fastpath+0x16/0x1b
[78112.153930]
[78112.154028] Restarting tasks ... done.
[78112.393352] forcedeth 0000:00:0a.0: irq 43 for MSI/MSI-X
[78112.393542] eth0: no link during initialization.
[78112.394312] ADDRCONF(NETDEV_UP): eth0: link is not ready
[78112.839051] EXT4-fs (sda4): re-mounted. Opts: errors=remount-ro,commit=0
[78112.858386] EXT4-fs (sda7): re-mounted. Opts: commit=0
[78112.869057] EXT4-fs (sda6): re-mounted. Opts: commit=0
[78123.400333] eth2: no IPv6 routers present

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: modemmanager 0.4+git.20100809t153145.be28089-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-30.54-generic 2.6.35.13
Uname: Linux 2.6.35-30-generic x86_64
NonfreeKernelModules: nvidia wl
Architecture: amd64
Date: Sat Jul 23 11:56:34 2011
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: modemmanager