I feel like this is a question I should be able to answer, but can't, so I figured I would ask the gurus here:

If a mage casts a spell with range "touch" on someone else, and wants to sustain the spell, do they need to maintain physical contact, or do they only need touch to put the spell in place?
For that matter, if a mage looses LOS on the target of a LOS spell, can they still sustain it?

My intuition says they need to maintain the correct range to sustain the spell, but I vaguely remember reading something that said they did not somwhere.
I tried a quick search, and did a pass in SR4A and Street Magic, and I can't find the answer, so if anyone can point me to the relevant rule, I would greatly appreciate it.

Okay, but do either of you have a page reference for this? I'm happy to go with this rule, but I'd be curious if it is actually spelled out anywhere.

Step 7: Ongoing Effects
Many spells can be sustained for as long as the magician is willing
to concentrate on the spell, as noted in the spell’s Duration. While
sustained spells do offer the opportunity to have an ongoing magical
effect, they are also draining on the magician’s magical abilities. For
each sustained spell the magician maintains, she suffers a –2 dice penalty
on all other tests.
If an area-effect spell is sustained, the affected area may be moved
with a Complex Action, as long as it remains within line of sight.
Characters who “drop out” of the affected area are no longer affected
by the spell; characters who are “enveloped” by the area must defend
against the effects of the spell as appropriate.
If the gamemaster chooses, certain circumstances may threaten to
break a magician’s concentration while she is sustaining a spell, such as
taking damage, full defense, dropping prone, and so on. If a magician’s
concentration is disrupted while sustaining a spell, she must make a
Spellcasting + Willpower (2) Test to avoid dropping the sustained
spell (note that the sustaining modifier does not apply to this test).

It's also been stated here on the boards by dev types that like spirit powers, spells have to meet the activation / usage requirements. Once that is done, they then follow their duration criteria. Sustained spells stay active so long as the caster is sustaining them.

It was also said that sustaining of powers / spells can be across the Physical / Astral Boundary as it's just keeping the mana conduit open once it is established by the act of casting / activating.

In previous versions didn't one have to drop all sustained spells to switch between astral projection and meat bod? Don't recall seeing that in 4th though.