ceceo/thetheo
I know that some parts of the spanish speaking world 'lisp' the letters 'c' and 'z' but not 's', but I have heard the 's' being 'lisped' in some words too, do you 'lisp' the 's' when it is next to a 'c' or a 'z' like in 'escuchar'? And where are these 'lisped'/not 'lisped'? It's one of my favourite things about the language, I just don't know very much about it 
5 Answers
Distinction : refers to the differentiated pronunciation of the two Spanish phonemes written ‹s› and ‹z› or ‹c› (only before ‹e› or ‹i›, the so-called "soft" ‹c›):
1. ‹s› is pronounced as a /s/ like in English
2. ‹z› and soft ‹c› are pronounced as (the ‹th› in think).
This pronunciation is the standard on which Spanish orthography was based, and it is universal in Central and Northern parts of Spain, except for some bilingual speakers of Catalan and Basque. Thus, in Spanish the choice between the spellings ‹sa›, ‹se›, ‹si›, ‹so›, ‹su› and ‹za›, ‹ce›, ‹ci›, ‹zo›, ‹zu› is determined by the pronunciation in most of Spain, unlike English, where it is often done according to etymology or pure orthographic conventions
Ceceo is a phenomenon found in a few dialects of southern Spain in which the historical phonemes /s/ and /?/ are both realized as [?]. In other words, only the latter sound is used for ‹s›, ‹z›, and soft ‹c›. Ceceo is found primarily in some varieties of Andalusian Spanish, although there is some evidence of it in parts of Central America.
Seseo is the merger in the opposite direction: the original phonemes /s/ and /?/ are both pronounced as [s]. Seseo is the most widespread pronunciation among Spanish speakers worldwide. Although a minority pronunciation in Spain, virtually all speakers in Hispanic America are seseantes, and seseo is considered standard in all varieties of Latin American Spanish. It does coexist with distinción and ceceo in parts of Spain (e.g. in some areas of Andalusia). Traditional dialect atlases show one variant or another used in adjacent regions. In Spain, seseo is considered "more socially acceptable or perhaps 'less substandard' than ceceo."[1]
The following table gives an example of the three pronunciation patterns discussed so far:
la casa "the house" la caza "the hunt"
distinción /la ?kasa/ /la ?ka?a/
ceceo /la ?ka?a/ /la ?ka?a/
seseo /la ?kasa/ /la ?kasa/
Castilian lisp
A persistent urban legend claims that the prevalence of the sound /?/ in Spanish can be traced back to a Spanish king who spoke with a lisp, and whose pronunciation spread by prestige borrowing to the rest of the population. This myth has been discredited by scholars for lack of evidence.
As gfreed mentioned, in Spain we don't think that pronouncing Cs/Zs and Ss differently is a "lisp". Much to the contrary, that distinction is an evolution of the original pronunciation of Spanish, although it used to be even more complex several centuries ago. Over time it evolved differently in different regions of Spain, to "distinction" in some regions (in most, actually), and to "neutralization", or pronouncing all those letters as either s or th, in some parts of southern Spain. Since it seems that many of the "conquistadores" exported the second variation, which in the whole of Spain was spoken by a minority, to latin america, it stuck there and "distinction" remained a local phenomenon.
Incidentally, in much of Spain it is considered a lisp to talk as some Andaluces, who instead of neutralizing those letters to s like in south america, they neutralize them to th, or "ceceo".
Galsally is correct in her comment that ´c´is pronounced ´th´before 'e' or 'i' and the pronunciation is generally used by natives on the Peninsula and that is the way we are taught. You can, however, be just as well understood if it is pronounced 's' as we have many South American immigrants here who speak that way. In the Cadiz region the lisp on 'c' and 'z' is very strong. To my ears it sounds very attractive although I struggled with the word 'cerveza' for a while.
I have posted this before, I'm sure you'll find it interesting as I did.
SD thread about pronunciation of 'z'
Also you could type in a search, it is a frequently asked question and this is one example.
There is little to add here, but people from Spain would find the term "lisp" insulting for two reasons: first, because "lisp" is a mispronunciation, and the pronunciation is standard in Spain and taught at schools. The second reason is that some people in Spain do have a lisp, but that means that they are using the "th" sound where the "s" sound should have been used.
