Most of the thieves quests, are located where there is a guild,

http://www.uesp.net/wiki/Morrowind:Thieves_Guild#Thieves_Guild_Quests

So, in ABM you can select targets for the thieves guild only in these cities (Balmora, Vivec, Sadirth Mora, ALd Ruhn).

Should this change? Could I select targets in Suran, Caldera, Tel Mora etc.. and then go to the nearest guild and assign the job to a thief?

and how about towns that are far from any guild, like Dagon Fel?

Seem to remember being sent to Hla Oad for one Thieves guild quest quite early on ( Sugar lips sends you ) and , though it IS just down river from the quest givers location , well.....Maybe towns in the same vicinity but not ones that require lots of travel .

I think that you should be able to employ a thief regardless the location. The guilds will just pass the contract to their nearest location and local member will take care of the rest.

since when to thieves care about rules and boundaries? lol

I don't think they'd steal from anybody on Solstheim or in Mournhold, but anywhere else should be fair game. Perhaps you should increase the price depending upon the distance of the job from the nearest thieves hide-out.

The http://www.uesp.net/wiki/Morrowind:Honor_Among_Thieves, unlike the greasy Camonna Tong. They don't kill their targets for instance. Man, I'm just feeling disagreeable with you today, gjerkson.

And to comment on topic. I'd like to think that each guild hall has a field of influence. So the Balmora group will go to Hla Oad and Caldera for instance.